ORLD WITHOUT GRAVITY AW SP-1251 World without Gravity CONTENTS Fore word 1 CHAPTER 1. INTRODUCTION...

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– Research in Space for Health and Industrial Processes –

byGünther Seibert et al.

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Contact: ESA Publications Divisionc/o ESTEC, PO Box 299, 2200 AG Noordwijk, The NetherlandsTel. (31) 71 565 3400 - Fax (31) 71 565 5433

A WORLD WITHOUT GRAVITY

By

G. Seibert et al.

Editors: B. Fitton & B. Battrick

A World without Gravity

SP-1251June 2001

SP-1251: A World Without Gravity

Published by:ESA Publications DivisionESTEC, PO Box 2992200 AG NoordwijkThe Netherlands

Editors:Brian Fitton & Bruce Battrick

Design & Layout:Carel Haakman

Copyright:© 2001 European Space AgencyISBN No.: 92-9092-604-XISSN No.: 0379-6566

Price: 40 Euros/90 DflPrinted in: The Netherlands

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Preface

The principal task of the European Space Agency is to develop and to operatespaceflight systems for research and applications and, in doing so, to promoteEuropean and international co-operation. One of the Agency’s major programmes isthe European participation in the building and operation of the International SpaceStation (ISS). The ISS is the largest science and technology venture ever undertaken inspace. Its assembly started in late-1998 and will last until early 2005, at which pointthe routine utilisation and exploitation phase will begin. However, access will beavailable to some research facilities on the ISS from 2002 onwards.

A major motivation for Europe to participate in the development and utilisation of theISS is that this unique laboratory in space opens up a new era of research in the fieldof life and physical sciences and applications in space. For the first time, Europeanscientists and industry will have routine and long-term access to a wide range ofsophisticated experiment equipment and facilities in space, with laboratory-likeworking conditions. Experimenters who utilise the weightless conditions of space –the so-called ‘microgravity environment’ – will find outstanding opportunities toexpand their research, to the eventual benefit of both industry and human health andwelfare.

Microgravity research has been undertaken in Europe for more than 20 years, throughboth ESA and national programmes. Today, the life- and physical-sciencescommunities are mature, well-established and organised at the highest scientific level,as recently confirmed by the European Science Foundation. These user communitiesare of vital importance for ISS utilisation. The continuous research opportunitiesoffered by the ISS provide excellent prospects for the futures of these research fields,which are closely related to industrial needs and health-care requirements on Earth.

Research in space life and physical sciences has benefited strongly in past years fromactive international co-operation. The new era that lies ahead will allow us to enhancethis cooperation on a global scale, which will certainly further improve the quality ofthe scientific and technological undertakings.

The ESA-developed Spacelab, flown successfully many times over a 15-year period onthe Space Shuttle for missions lasting typically 10 days, was until 1998 the‘workhorse’ for microgravity research. Today, the advent of permanent access to theISS’s laboratories and external platforms is providing a strong incentive to expand the

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CONTENTS

Foreword 1

CHAPTER 1. INTRODUCTION

1.1 The Motivation for Research in Microgravity 5

1.2 Access to Microgravity Conditions 16

1.3 European Manned Spaceflight and Microgravity Research 25

CHAPTER 2. ASPECTS OF CURRENT MICROGRAVITY RESEARCH

2.1 Changes to Human Physiology in Space, and Space Medicine

2.1.1 The Cardiovascular System 352.1.2 Pulmonary Function in Space 482.1.3 Fluid and Electrolyte Regulation and Blood Components 582.1.4 Muscles in Space 692.1.5 The Skeletal System 832.1.6 The Human Sensory and Balance System 93

2.2 Space Biology

2.2.1 Cell and Molecular Biology 1112.2.2 The Role of Gravity in Plant Development 1212.2.3 Exobiology: The Origin, Evolution and Distribution of Life 137

2.3 Physical Sciences and Applications

2.3.1 Macromolecular Crystallisation 1592.3.2 Crystal Growth of Inorganic Materials 1722.3.3 Microstructure and Control in Advanced Casting Processes 186 2.3.4 Heat Transfer and the Physics of Fluids 2112.3.5 Critical-Point Phenomena 2272.3.6 Interfaces, Foams and Emulsions 2412.3.7 Combustion 2542.3.8 Complex and Dusty Plasmas 2682.3.9 Vibrational Phenomena in Fluids and Granular Matter 2852.3.10 Cold Atoms in Space and Atomic Clocks 292

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scientific research activities. At the same time, there is an initiative also to involveEuropean industry much more and to encourage a move from fundamental researchto application projects.

One person who has been actively involved in the definition, approval and executionof microgravity research at the European level, from the very beginning in 1982 untilhis recent retirement from ESA, is Günther Seibert. He therefore has unique experiencein this field and a detailed knowledge of the research areas, as well as excellentcontacts with the microgravity research community, European space industry, thenational space agencies and our international partners.

When Günther Seibert retired as Head of the Microgravity and Space StationUtilisation Department, I thought it a good idea to ask him to take the opportunity ofhis retirement to work on a book that would exploit his in-depth knowledge andexperience of his field to provide an overview of European microgravity research, andthe various national and international programmes. It would provide a uniqueopportunity to document the history of European microgravity activities, and toreport on past achievements and on the current status of this field both for basicresearch and for industrial R&D.

The publication of this book comes at a time that marks the transition between thepioneering days of experiments on Spacelab, and the Space Station era of permanentaccess to research laboratories in space. It comes too at a time of decision, when thefuture level of European activities on the ISS will be defined by the next EuropeanSpace Conference at Ministerial Level. In that context, it is hoped that the wideperspective of this book and its non-specialist approach will be valuable to those whoare charged with preparing for those important decisions.

J. Feustel-BüechlDirector of Manned Spaceflight and Microgravity European Space Agency

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CHAPTER 4. THE GROWTH OF MICROGRAVITY RESEARCH– From Skylab to the International Space Station

4.1 The Origins of Microgravity Research in Space

4.1.1 Early US and Soviet Activities 367– The Skylab Programme– The Apollo-Soyuz Test Project– The Soviet Salyut Orbital Station– The Mir Space Station– Guidelines for Microgravity Research in the USA

4.1.2 Early European Microgravity Activities 372– The Joint US – European First Spacelab Mission– Early European Spacelab Experiment Facilities

4.1.3 The European National Programmes 378– The German Microgravity Programme– The French Microgravity Programme

4.2 The ESA Microgravity Programmes

4.2.1 Towards the First ESA Microgravity Programme (Phase-1) 3884.2.2 Phase-2 of the ESA Microgravity Programme and Its Extensions (EMIR-1) 3904.2.3 The ESA EMIR-2 Programme, Its Extension and Applications Projects. 3944.2.4 The ESA ‘Microgravity Facilities for Columbus’ (MFC) Programme 396

CHAPTER 5. THE FUTURE OF MICROGRAVITY RESEARCH

5.1 Microgravity Experimentation in the Space-Station Era

5.1.1 Introduction 3995.1.2 The ISS: an International Endeavour 400

– Scientific Research– Application-Oriented Research– Operational Considerations and Constraints– Complementarity with other Research Opportunities– The First Experiments on the ISS– Future Outlook

5.2 Major ESA Microgravity Facilities for the ISS

5.2.1 Introduction 408

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CHAPTER 3. FROM BASIC RESEARCH TO COMMERCIAL APPLICATIONS

3.1 The Scope and Impact of Information and Technology Transfer

3.2 The Commercial Spin-Off from European Microgravity Research

3.2.1 Glaucoma Diagnosis: the ‘Selftonometer’ 3083.2.2 Osteoporosis Diagnosis: the ‘Osteospace’ 3103.2.3 Video Oculograph 3113.2.4 Ozone Disinfection: the ‘Sterlite’ 3123.2.5 Triple-Containment Glovebox 3133.2.6 Heat Exchanger 3143.2.7 Respired Gas Analyser 3143.2.8 Waste-Management Devices 3163.2.9 Three-Dimensional Eye Tracker 3173.2.10 Ultrasonic Components 3193.2.11 Mobile Photogrammetric Measurement System 3203.2.12 Crash Tester for the Car Industry and Railway Electrical Monitor 3213.2.13 Body-Fluid Monitoring with Multi-Frequency Impedance Measurements 3223.2.14 Posture Platform and Locomotion Measurement System 3243.2.15 Future Developments 3253.2.16 Spin-Offs: Impact on Jobs and Company Creation 3333.2.17 Conclusions 334

3.3 European Industry and Microgravity Experimentation

3.3.1 Introduction 3383.3.2 Applied Research in Space of Industrial Interest 339

– Measurement of Thermo-physical Properties of Melts and Other Fluids– Solidification Behaviour of Metals and Alloys – Crystal Growth of Semiconductor and Sensor Materials– Growth of Protein Crystals and Other Large Biomolecules– Combustion Research– Ceramic and Metallic Powders– Micro-encapsulation– Tissue Engineering

3.3.3 Industry’s Attitude to Research in Space 3533.3.4 The ESA Microgravity Application Promotion (MAP) Approach 3563.3.5 Selected MAP Projects 3583.3.6 Industry-Oriented Space Research and the European Commission 3633.3.7 Conclusions and Outlook 364

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5.2.2 ESA Microgravity Facilities in the Columbus Laboratory 411– Biolab– Fluid-Science Laboratory– European Physiology Modules– Materials-Science Laboratory– Electro-Magnetic Levitation Furnace– European Drawer Rack– Protein-Crystallisation Diagnostics Facility

5.2.3 ESA Facilities and Equipment in the US Laboratory 423– Muscle-Atrophy Research and Exercise System– Percutaneous Electrical Muscle Stimulator– Hand-Grip Dynamometer and Pinch-Force Dynamometer– European Modular Cultivation System– Biotechnology Mammalian Tissue Culture Facility– Pulmonary-Function System– Physical-Sciences Equipment

5.2.4 ESA Microgravity Experiment Equipment for ISS External Platforms 431– Exobiology Experiment Unit (Expose)– Atomic Clock Ensemble in Space (ACES)– Body Radiation-Dosage Measurement Unit (Matroshka)

5.3. A Future European Life- and Physical-Sciences Research Programme

5.3.1 Introduction 4365.3.2 A User-Driven Programme 4365.3.3 The Selection of Research Objectives 4375.3.4 The Alignment of Strategic Objectives with Other European Institutions 4395.3.5 Consolidation of a European Strategy with the National Authorities 4415.3.6 The Role of European Industry 4415.3.7 Explaining to the General Public 442

6. APPENDIX

6.1 Programmatic Structure of ESA’s Microgravity Activities 4436.2 ESA Facilities on Spacelab and Spacehab 4456.3 ESA Experiments and Facilities on Bion/Foton 4496.4 ESA Microgravity Experiments and Facilities Flown on Mir 4526.5 Summary of Missions, Facilities and Experiments 4566.6 Short-Duration Flight Opportunities 4596.7 The European Retrievable Carrier (Eureca) and Its Payload 4686.8 Future Experiments and Microgravity Application Projects (MAPs) 472

Acknowledgements 493List of Contributors 494

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Foreword

When in early 2000 Mr Feustel-Büechl, ESA’s Director of Manned Spaceflight andMicrogravity, proposed that I should compile a book on the activities and results ofpast microgravity research, hardware development and programmatic aspects andprovide an outlook on the future International Space Station (ISS) utilisation era, I wasinitially hesitant and agreed only after further reflection. My initial hesitation wascaused by the fact that space research in the life and physical sciences is a multi-disciplinary activity that has resulted in many incremental new findings, extensions toour knowledge and considerable technological progress, rather than in just a fewspectacular breakthroughs. I therefore concluded that it would only be possible topaint a true picture of the scientific, technological and biomedical progress achievedso far by soliciting contributions and assistance from the large number of scientistsinvolved, many of whom are distinguished experts in their respective fields. It was alsoobvious to me, having been involved from the humble beginnings of European life- andphysical-sciences research activities on manned and unmanned space missions, thatthe task in prospect was huge, involving as it did the compilation of a large amount ofdata on experiment facilities and spacecraft, programmatic details and historicalevents.

In contrast to the fields of space astronomy, planetary exploration or remoteobservation of Earth, where the discoveries can often be shown in the form of excitingphotographs, scientists working in the microgravity-research disciplines have no easyvisual means of justifying the costs of their labours. The readers of this book willtherefore hopefully be somewhat patient as we try to stimulate their interest in andexcitement about this still rather new area of research. To facilitate this process, wehave provided an extensive Introduction (Chapter 1) to try to explain in simple termswhy this kind of research is of increasing interest, and how many questions with far-reaching implications for mankind can be answered in laboratories in space.

The nine life-sciences and ten physical-sciences sections of Chapter 2, entitled ‘Aspectsof Current Microgravity Research’, have been written by more than 30 Europeanscientists (see List of Contributors). They were asked to outline the past achievements,current status, and the future importance of space in the research field that theyrepresent, with special emphasis on recommendations for future work in thatdiscipline. These contributions were also reviewed for completeness by otherscientists working in the field.

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A total of 30 people of different nationalities and with quite different professionalbackgrounds have contributed to this book, which has been written for the ‘educatednon-expert’. This means that the use of equations, specialised terminology, and formalscientific referencing has had to be minimised, which was an unusual requirement formost of the scientific contributors.

Taking into account all of these multi-faceted, multi-national inputs and therequirement not to write a scientific textbook, but rather a ‘Scientific American style’volume, I soon came to the conclusion that an experienced English-mother-tongueexpert with a broad scientific background would be needed to harmonise thepresentation of the various contributions. Fortunately, Dr. Brian Fitton, who hadalready been involved in the scientific editing of several ESA-supported microgravitypublications, was prepared to take on this difficult work. He also helped me to writeChapter 1 (Introduction), which addresses the important role that gravity plays forliving organisms and the effects of microgravity conditions on basic physicalphenomena through the quasi-suppression of buoyancy-driven convection in fluids, ofsedimentation, and of hydrostatic pressure gradients, for example. Chapter 1 alsosummarises the role that the absence of gravity plays in the major microgravity-research disciplines of biology, physiology, fluid and materials sciences, biotechnologyand fundamental physics. Furthermore, it addresses the topic of access tomicrogravity conditions and gives a synopsis of European Manned Spaceflight andMicrogravity Research.

Günther Seibert

Chapter 3 addresses the important topic of the transition ‘From Basic Research toCommercial Applications’. It includes the impact of information and technologytransfer (3.1) and an extended section (3.2) on the spin-offs from microgravity researchthat are already on the commercial market, and on expected future developments inthis field of technology transfer. Many of the technical and economic data provided onthese spin-offs are based on interviews conducted during visits to some 25 companiesand research institutes involved in hardware development for life- and physical-sciences research in space. The commercial sales value of these spin-offs in 2001 isestimated to be 50–60 million Euros, and for 2002 this figure climbs to 90–100 millionEuros. Since industrial research in space by non-space industry has become – in viewof the future utilisation and exploitation of the ISS – an issue of major politicalimportance, I asked Dr. H. Sprenger, a long-standing expert in this subject, tocontribute a section (3.3) entitled ‘European Industry and MicrogravityExperimentation’.

Chapter 4 describes the history of research under microgravity conditions from itsorigins on early American and Soviet space missions, up to the preparations for theutilisation of the ISS. It covers the early European microgravity activities performedwithin the framework of ESA missions and at national level, and recounts the initialdifficulties encountered in setting up and funding a European programme.

Chapter 5 looks at the future of microgravity research. It addresses the differencesbetween conducting research on the ISS and that performed during the Spacelab era(5.1). It also describes all of the major European experiment facilities presently underdevelopment for the pressurised laboratories and external platforms of the ISS (5.2).Thereafter, the strategy and basic principles underlying the planned future Europeanlife- and physical-sciences research programme are discussed (5.3).

In order to ensure the inclusion of the very latest research plans and programmeproposals for future life- and physical-sciences programmes within ESA, I asked Dr. M. Heppener, Head of the ISS Utilisation and Microgravity Promotion Division, tocontribute two sections (5.1 and 5.3), entitled ‘Microgravity Experimentation in theSpace-Station Era’ and ‘A Future European Life- and Physical-Sciences ResearchProgramme’.

Chapter 6 is presented in the form of an Appendix, because it not only provides detailsabout the programmatic structure of ESA’s microgravity activities, but also gives alarge amount of scientific and technical information in the form of tables onexperiments and facilities flown on Spacelab, Spacehab, Bion/Foton, Mir, short-duration flight opportunities (i.e. mainly sounding rockets) and the EuropeanRetrievable Carrier (Eureca). Chapter 6 also lists the Microgravity Applications Projects(MAP) selected by ESA in the form of tables for the life- and physical-sciences andbiotechnology fields.

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CHAPTER 1INTRODUCTION

B. Fitton and G. Seibert

1.1 The Motivation for Research in Microgravity

Gravity has shaped our world, defined the way that we live, and governs the veryprocesses of life itself. It gives rise to the basic phenomena of sedimentation,buoyancy and convection flows and it causes hydrostatic pressure. It influences suchthings as the movement of blood and the body-fluid distribution, how we breathe,keep cool and how we move. Acting on the body’s sensors, it establishes our postureand our orientation. We are creatures of the Earth’s gravitational field and the sense ofweight that it gives to our body’s mass.

What happens then to the human body when the influence of gravity is removed? Thiswas the question that concerned the pioneers of manned spaceflight. Can a humanactually withstand the sudden entry into the weightless conditions of orbital flightwithout suffering a catastrophic body-function failure?

To answer that, attempts were made to create weightless conditions on Earth.However, such attempts are necessarily of limited duration, since the test object hasto be placed in a condition of free fall, essentially as if in a freely falling lift, for it tocease to perceive the effects of the Earth’s gravity field and become weightless. Thatcan be achieved for only a few seconds in an evacuated drop tower. Slightly longerexposure to weightless conditions can be obtained by flying an airplane over aparabolic trajectory. Towards the top of the parabola, the airplane and contents entera free-fall regime, lasting about 20 seconds. Similarly, the ballistic flight of a soundingrocket can be used to provide weightless conditions lasting up to some 15 minutes.

But the only way to establish long-term weightless conditions is actually to go intospace. There, a freely drifting spacecraft and its crew are in a permanent free-fallenvironment, since gravitational and inertial forces are counterbalanced and inequilibrium. In the particular case of a spacecraft in a stable orbit around the Earth,the inward pull on it and its contents due to gravity is countered by the outward thrust


Consequently, gravity would be expected to exert an influence through its effects onfluid flow, sedimentation and its modification of the behaviour of thin liquid films. Byremoving the effects of gravity, it is possible to investigate the changed cell activityand function. Different gravity levels can then be applied, using a centrifuge, to followthe sequence of these changes and elucidate the mechanisms at work.

Experiments of this type have shown that the cellular machinery is sensitive to subtlemodifications in its mechanical and biochemical micro-environment as the level ofgravity is changed. In plants, the equal partitioning of the genetic material at celldivision is disturbed and chromosomal abnormalities are introduced, implying thatplant cell proliferation requires positional cues from gravity. Other effects on plant andanimal cells include changes to the proliferation rates, energy metabolism, cellmembrane composition and function, cell and tissue differentiation, and the rate ofcell ageing.

There is currently considerable debate as to the extent to which these observed changesare the result of a direct perception of gravity, through its effect on structures within acell, or are due to an indirect effect operating through induced changes in the cell’sphysical and chemical environment. In view of the fundamental importance of theseresults and the potential insight into cell mechanisms, there is considerable motivationto develop these studies and seek further clarification of the mechanisms at work.

The direct perception of gravity undoubtedly takes place at the cellular level in thosespecialised cells and unicellular organisms that use gravity for orientation andmovement. For example, gravity-sensitive cells in higher plants are continuouslystimulated and control the direction of growth via gravity-dependent mechanismssuch as the sedimentation of high-density particles within the cell. The cells at the endof root tips appear to sense the gravity vector by this means and guide the root growthdownwards. The value of space experiments in this class of cell lies in exploring thedetailed physical and biochemical processes at work in gravi-perception and response.

- Human Physiology

As yet it is uncertain whether changes that have been observed in individual humancells when cultured under microgravity conditions, could actually manifestthemselves as discernible physiological changes in the whole body. On the other hand,when searching for the origins of the many reactions of the human body to weightlessconditions, it is generally necessary to consider processes occurring at the tissue,cellular and molecular level. This is particularly true in the case of the bone mass-lossprocess, which has been well documented in astronauts and which does not appearto have an end point. It is potentially the most damaging of the physiological changesobserved in response to microgravity, with an origin in a changed bone-cellenvironment and metabolism.


of the centrifugal force. A body’s weight in that spacecraft therefore becomes zero, asthat pull of gravity is effectively neutralised.

So with very little guidance gained through the use of short-duration experimentsunder weightless conditions, the daunting step into spaceflight was taken in thoseearly days – first using test animals, and then finally with some very brave men.

Fortunately those early, albeit brief, manned flights showed that there was noimmediate danger to life from weightlessness. However, a large number of importanteffects were detected which required further study. It became evident that spaceflightinfluenced many aspects of the functioning of the human body, including the heartand lungs, the stress-bearing bones and muscles, and the nervous system. Theseeffects were seen as a potential risk to astronaut health on long-duration space flights.Consequently, astronaut health and long-term survival were the motivation for someof the earliest research in weightless conditions – or ‘microgravity’ as it is generallycalled. Most of that research was therefore centred on human-physiology studies andwas concerned with the macroscopic effects on the body. Only later did researchextend to exploring the process of change down to the microscopic level. With thatextension came a broadening of the research into general biology and exobiology.

A similar evolution occurred in the study of fluid behaviour in microgravity. The firstsimple experiments on Skylab were largely concerned with demonstrating thechanges in behaviour at a macroscopic level, as the influence of gravity was removed.It was only later, with the opportunity to fly more sophisticated experimentalequipment, that it became possible to perform more structured experiments toexplore in detail the changes in fluid behaviour and to undertake controlledexperiments on liquid/solid interfaces, particularly in crystallisation.

In all such experimentation, gravity is regarded as a parameter and a possiblevariable. Its removal can illuminate the nature and extent of its direct effects, as inmany human physiology experiments. Its absence may also reveal the existence ofother underlying yet important processes, which are otherwise obscured andimpossible to observe. Similarly, the removal of the gravity-associated effects ofsedimentation, thermal convection and hydrostatic pressure provides an opportunityto establish unique conditions to probe basic processes.

- Biology

The early observation that gravity influences the basic processes of life is hardlysurprising, since gravity has been an ever-present influence during the creation of lifeand in its evolution over the past 3.5 billion years. All life forms are principallycomposed of liquids and use surfaces to isolate their different constituents, as well asto facilitate and control the myriad reactions that support the processes of life.

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Careful investigation of these and related processes in microgravity constitutes avaluable tool with which to extend the understanding of basic body-fluid regulationprocesses involving the kidneys, the glandular system, and the heart.

The human respiratory system and its functioning also undergo changes in space.There are changes in the chest-wall mechanics, the relative displacement of the ribcage and the abdominal compartments as gravity is reduced. The details of lungventilation and blood perfusion patterns remain to be further investigated, takingadvantage of the lack of gravity to clarify the basic processes. Similarly, the mechanicsof breathing and the neuro-physiological adaptation of the respiratory system, as itencounters low gravity and radically changing biomechanical conditions, need to bestudied further.

Amongst the profound changes to the human body on encountering weightlessconditions, that of disorientation and the often-accompanying nausea in the first fewdays is particularly debilitating. The cause lies in the disturbance to the acceleration-sensing system of the inner ear, a system that registers the force of gravity andcontributes to defining posture and balance on Earth. There are also visual orientationillusions and feelings of self-inversion, which originate in the loss of appropriatesignals from the mechanical receptors in the muscles, tendons and joints and from theskin pressure sensors, especially on the feet.

The progressive adaptation of astronauts to this environment indicates that thenervous system can compensate for the loss of gravitation-induced stimuli. It does soby neuronal plasticity, in which the nerve cells react to new conditions by changingcellular dimensions and making new connections or adapting earlier ones. In otherwords, the phenomenon of neural plasticity amounts to a learning process. Thequestion has been to what extent the peripheral neural system, involving the gravitysensing mechanisms, is included in this learning process, as distinct from the centralneural system?

Space experiments have shown that in the inner ear the adaptation to microgravityconditions occurs largely by a progressive increase in the number of communicationsites lying between the gravity sensor cells and the nerve fibres ending on them. Thisobservation of rapid adaptation, starting within hours of exposure to a newenvironment, confirms that these peripheral sensory elements do indeed learn andrespond rapidly to the changed environment. Such information has potential value inthe treatment of balance disorders on Earth, a problem that afflicts millions of people,as well as having direct relevance in improving the welfare of astronauts.

Much more radical changes in the structure and connections of the nerve cells occurduring the early development of the nervous system. As those changes are regulatedby mechanical and biochemical factors, it is thought that gravity may play an


This changed bone-cell environment is initiated following the acute loss ofgravitational loading of both bone and muscle in the weightless conditions. There is arapid onset of mass loss, especially in the load-bearing bones. This is accompanied byan elevation of calcium levels in the blood, which carries a potential risk of damagingeffects in terms of kidney stones and calcification of the soft tissue in the longer term.The bone mass loss continues unabated throughout the time in orbit, at a rate ofabout 1% per month. This currently sets a limit to the time that crews can safelyremain in orbit, if they are to avoid serious risk of bone fractures on return to Earth.

The precise mechanisms driving this bone-loss process and those causing theaccompanying muscle atrophy are still uncertain. Bone is in a dynamic equilibriumbetween bone growth and destruction - an equilibrium that can be disturbed byfactors such as hormones and vitamins in the blood, as well as by the changedmechanical stressing of the bone.

Weightless conditions may modify all of these factors, but it is likely that the basicprocess follows from the unloading and reduced stressing of the bones and muscles,which modifies the stretch-activated chemistry at the cellular level. Exercise regimeshave had little success in retarding bone mass loss and muscle atrophy. Futureresearch in this area will therefore probably seek a solution by modifying thebiochemistry at the cellular level. In so doing, it is quite possible that the knowledgegained may contribute to easing of the problems of bone mass loss in the elderly andin post-menopausal women on Earth.

There are other physiological changes observed in astronauts that also bear somesimilarities to those that develop as a result of the normal ageing process on Earth,such as the de-conditioning of the cardiovascular system and an apparent depressionof the immune system’s response to infection. The difference of course is that thechanges in space begin to occur rapidly upon entering a weightless condition and theyafflict a young healthy person. Consequently, investigations made under theseconditions give, to some degree, an accelerated view of certain ageing symptoms in asubject free from other complicating ageing characteristics. Such investigationsshould assist in furthering the understanding of aspects of the normal ageing processand, in the development of countermeasures for astronauts, may also aid in relievingthe symptoms in the aged.

There are other changes in the human body in weightlessness, whose study will likelylead to new insights into fundamental physiological processes and promote a betterunderstanding of the body’s functioning at a basic level. For example, the rapidupward displacement of body fluids that occurs when the downward pull of gravitydisappears, automatically triggers responses in heart and kidney functions. There is anincrease in fluid and electrolyte excretion by the kidneys and an increase in the bloodbeing pumped by the heart, together with a redistribution and reduction of plasma.

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telluride and gallium arsenide. Similarly, the influence of gravity-induced effects in thetransport of material during vapour growth of semiconductor crystals and epitaxiallayers, used in electronic device production, is being studied and related to thecreation of defects that can limit device performance.

Despite its fundamental importance in the basic process of materials production, theunderstanding of how the growth of crystals and micro-crystals is initiated bynucleation is still rudimentary, especially in the case of multi-component commercialmaterials. The lack of accurate knowledge of the basic thermo-physical properties,such as density, viscosity, diffusivity, thermal conductivity and specific heat, which isneeded to develop theories of nucleation, remains a major difficulty. Accurate thermo-physical data are also vital for numerical modelling of industrial processes in castingand crystal growth. The current figures for the viscosity of molten pure iron andaluminium, for example, are uncertain to within 50% and 100%, respectively. Thislack of reliable basic data for commercial materials, as well as those for fundamentalresearch, is largely due to the experimental problems arising from unwanted reactionsof the molten materials with container walls.

Containerless methods of holding the molten materials, which use electric,electromagnetic, or acoustic pressure retaining forces, can avoid this problem and arenow being used in ground-based studies. Their application in microgravity conditionsmeans that the force needed for containment is greatly reduced, thereby reducingdisturbances to the melt and greatly improving the accuracy of the data. Experimentsof this type have already provided precision thermo-physical data on highly reactivealloy melts, data that could not be obtained without the use of microgravity conditions.

These containerless facilities also lend themselves to the detailed study ofundercooling of molten materials and the production of metastable solids whosephysical properties may differ considerably from their stable counterparts. Suchmaterials may be crystalline structures, grain-refined and supersaturated alloys,disordered intermetallics, and quasi-crystalline phases.

All of these can provide innovative materials for engineering applications and thedetailed study of the fundamentals of their formation and growth using gravity-freeand containerless conditions will be invaluable.

The study of basic fluid-dynamics phenomena is greatly facilitated by the use ofmicrogravity conditions, since without the complications of gravity-driven convectionflows it becomes possible to test fundamental theories of three-dimensional laminar,oscillatory and turbulent flow generated by various other forces. The flows andinstabilities induced by surface-tension or thermal-radiation forces, together withdiffusive instabilities, can each be studied and all have substantial practical as well astheoretical interest.


important role in stimulating the proper development of the nervous system on Earth.For example, animals deprived of the opportunity to walk during the first weeks afterbirth never fully learn to walk properly. Studying how that development proceeds inanimals under weightless conditions will help define the respective roles of geneticdetermination and environmental experience. Understanding the nature of thesecritical periods of neural development has important implications for paediatrics. Itcould also help in the treatment of those suffering from neuromuscular diseases.

- Fluid and Materials Science

Although, historically, studies in the life sciences have been a major activity inmicrogravity research as outlined above, there has also been a considerableprogramme in fluid- and materials-science studies. This programme is continuing togrow. In Europe, the research has been deliberately focused by the science communityupon carefully selected topics that combine significant scientific interest with thepotential for improving industrial processes.

The changes in fluid behaviour in space lie at the heart of these studies in materialsscience. By removing gravity-induced effects, the experimental conditions can be greatlysimplified and the fundamental processes in fluids of many types can be more readilyexplored. With the consequent improvement in predicting and controlling the behaviourof fluids, particularly in regard to heat and mass flow, it becomes feasible to betterunderstand and then to improve a whole range of industrial processes that depend uponfluids. For example, the use of electromagnetic fields for convection flow suppression,stirring and shape control, is an important and well-established method for improvingthe industrial processing and control of growth from conducting melts on Earth.

This has applications in metal casting and semiconductor crystal growth. Theoptimisation of process conditions by numerical modelling is presently constrained bythe difficulty of simulating the heat and mass transport under turbulent conditions.Experiments using magnetic fields on melts in microgravity, under better definedconditions, will provide a clearer insight into the basic processes and aid in developingmore realistic models of the heat and species transport.

Through similar carefully designed experiments, it has also been possible to gain newinsight into the physical phenomena occurring at the growth interface in metallicmaterials and to improve the understanding of the processes by which the differentphases in immiscible metallic alloys separate and ripen. That understanding has led toits application in a current production process and future research will extend theseapplications.

Other research topics include the study of the factors controlling defect generationduring growth from the melt of commercially important materials such as cadmium

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dynamics of the processes involved is limited and inadequate to support thetechnological needs. By performing studies in microgravity, where thermal convectionprocesses and hydrostatic pressure are absent, other mechanisms operating can bestudied and quantified.

Dust particles are an inevitable product of industry, and of human activity in general.Much of it is classed as a pollutant. Yet in the form of powders they are also the verybasis of many industries, ranging from cement to flour. Hence a detailedunderstanding of such processes as aggregation is needed to improve the control andprocessing of these powders and to develop scavenging techniques for their removalfrom machinery and from air emissions. The study of the behaviour of dust andpowders in microgravity will provide basic information to aid ground-based researchby providing long-duration experiments with sedimentation processes, allowingstudies of aggregation in the absence of convection, of scavenging techniques, and thestudy of single-grain behaviour in collision processes.

Combustion processes involve chemical reactions with large temperature andconcentration gradients that lead to very strong convection-driven flows in gravityand to unstable burning. By contrast, controlled combustion experiments inmicrogravity offer the possibility to study the large steady flames that can exist in theabsence of convection flows. This allows the basic properties of the burning process tobe studied, together with the influence of various fuel types and fuel-injectionconditions. Droplet and particle burning under high-pressure conditions, such asoccurs in many propulsion systems, is another area for which microgravityexperiments can provide valuable basic information to support the modelling ofindustrial systems. Individual droplets can be isolated in space and the temperaturedistribution and chemical species concentration around the burning droplet analysedin a way that is impossible on Earth.

Almost three-quarters of the emissions of gases that potentially contribute to the‘greenhouse’ effect on Earth originate from combustion processes in industry, inpower generation and in motor transport. The study of combustion in microgravitycan provide valuable information, which complements terrestrial studies and willmake a significant contribution to improving the efficiency of those processes and inreducing the pollutant emission.

- Biotechnology

Biotechnology is the application and the commercialisation of biology. It is aninterdisciplinary field that draws upon the life sciences, the physical sciences, andengineering. It covers the practical application of biosystems at the tissue, cell, andsub-cellular component level, using controlled in-vitro or in-vivo operations inindustrial processes and in the management of the environment.


Supercritical fluids may also be better studied under microgravity conditions. Suchfluids are in a pressure and temperature regime that places them in an intermediateposition between gases and liquids, where they exhibit high density, low viscosity,very high compressibility and large diffusivity. They are therefore extremely sensitiveto hydrostatic pressure, which causes compression and stratification. Convection andbuoyancy effects also restrict the study of their fundamental properties and behaviouron Earth. Supercritical fluids are widely used in industry, for example as ‘solvents’ infood and in waste-management processes, and cryogenic gases, such as oxygen andhydrogen, are often stored as supercritical fluids. Consequently, there is considerableindustrial, as well as scientific, interest in the information derived from studies inmicrogravity of these remarkable fluids.

The absence in microgravity of hydrostatic pressure, which is the result of thecollective weight of each horizontal element in a liquid column, simplifies not only thestudy of supercritical fluids but also of normal fluids. For example, the heat and fluidtransport mechanisms involved in boiling can be more readily studied in depth andhave yielded some surprising data. Continuing studies have potential value for awhole range of applications in which empiricism has so far prevailed. Interfacialphenomena, phase transitions, and the flow behaviour of liquids in multiphasesystems, all of which are basic to many industrial processes, are open to investigationunder conditions that simplify their observation and analysis.

Many industrial processes involve the use of foams and emulsions, of adsorbed layersof surface-active components, or manipulate powders. The behaviour of thesematerials is strongly influenced by gravity effects, which masks some of theunderlying, but nonetheless important physical chemistry processes and these can beexplored in depth under microgravity conditions.

Liquid foams are formed by gas bubbles coming together to create a liquid-gas cellularstructure. They are created during many industrial processes, often as unwantedproducts needing control, but they are also the precursors of many solid foams, suchas polyurethane and the new metal foams. Their formation and many of theirproperties are controlled by the surface tension that acts at the liquid/gas interface.However, gravity significantly modifies the behaviour of the foam. Under microgravityconditions, it becomes possible to create stable uniform ‘wet’ foams. These then allowthe study of the action and dynamics of the surface-force-controlled processes in thecreation and in the draining of bulk foams, providing essential basic information tohelp predict and understand their behaviour under industrial conditions.

Reversible adsorption plays a fundamental role in many industrial and biologicalprocesses. The familiar experience of using detergents as a so-called ‘surfactant’ incleaning processes is but one of the many roles now played by this class of materials.Despite their increasing use to control surface properties, the understanding of the

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opportunities for successful research in this area of biotechnology. At the same time,the current basic research by European scientists into the detailed mechanisms thatcontrol the growth of protein crystals will be speeded up, so that commercial activitiescan be placed on a much firmer base.

- Fundamental Physics

There is now a growing interest in using the microgravity environment forfundamental physics. Several experiments are being considered, but the Europeanplan to place an atomic-clock assembly in space is of considerable importance in thecontext of both fundamental and applied physics.

Gravitation is a space–time property according to General Relativity, whose geometryis defined by the matter and the radiation it contains. Hence, a massive body such asthe Sun modifies the local space geometry by its presence, leading to the deviation oflight as it passes near to the Sun, and to retardation and frequency shifting of the lightemitted. Measurement of these effects depends upon the ultra-precise measurementof frequency and time using the cooled atomic clock, currently the world's mostaccurate timepiece. Its operation depends upon the cooling of caesium atoms to atemperature of about 1 micro Kelvin by a laser system that slows down their thermalvelocity. A microwave frequency is then locked into the resonance frequency of thecold caesium atoms. The final accuracy of this system depends upon the time forwhich a caesium atom can interact with this microwave field. On Earth, the caesiumatoms rapidly increase their speed when the lasers are switched off for signalinterrogation, due to gravity. This limits the interaction time and hence the final accuracy.

By going to the microgravity conditions in space, it is expected that the interactiontime will increase by a factor 10, and that the final time-measurement accuracy will beone to two orders of magnitude better than can be achieved by the best Earth-basedclocks. The ACES payload for the Space Station will combine such a clock withreference clocks and microwave and laser links to ground to provide a global timereference of unprecedented accuracy. In addition to its role in basic gravitationexperiments, it will also provide the time correlation for receiving stations in very longbaseline radio astronomy interferometry. The greatly improved timing accuracy willtranslate into improved angular resolution of remote stellar objects. It will also lay thefoundation for a new level of precision in Global Positioning Systems (GPS) and innavigation, and it will allow geodesy measurements of the Earth down to millimetreprecision.

- Conclusion

The preceding overview of current research in microgravity highlights not only thediversity and range of subjects, but also the extent to which the results of that


The applications domain is extremely wide. It ranges from the improvement andincreased control of environmental bioprocesses, through to the genetic enhancementof agricultural plants and to the understanding of the role of the cellular and tissuemicro-environment conditions in artificial bio-organ engineering. In addition,biotechnology covers the development of instruments, e.g. bioreactors, that arenecessary for the control of bioprocesses and for the sensing and support of thebiological functions of organisms.

The use of the microgravity environment of space for biotechnology research anddevelopment is already underway and will likely accelerate in the future, with theavailability of routine access to space via the International Space Station (ISS). Itsapplication in relation to current research into tissue engineering centres upon thesimplification, increased stability, and improved control of the fluid-based systemsinvolved in the cell micro-environment during cultivation and differentiation.

An example of this is the study of the role of cell density during in-vitro cartilagereconstruction, in the absence of any exogenous supporting structure. On Earth, themaintenance of the necessary cell density without a matrix support is defeated by thesedimentation of the suspended cells in the bioreactor chamber. By studying a matrix-free growth in microgravity, it is possible to avoid the risk of undesirable chemicalsignalling due to the use of natural scaffolding, or the complications induced bydegradation of a synthetic re-absorbable scaffold. Because of the extremely highcontent and organisation of exopolymeric material in cartilage, this may be the onlymeans for in-vitro production of a functional cartilage analogue.

Of many other current activities, those relating to eventual drug development are ofparticular interest and involve protein crystal-growth studies. An accurate knowledgeof the three-dimensional structure of proteins, of which there about a million differenttypes, is required in order to have a full understanding of the function of each one. Asyet, only a small percentage of these protein structures have been determined. Amajor difficulty has been the lack of large crystals of sufficient crystalline quality toallow accurate X-ray determination of the structure.

It was expected that the absence of sedimentation and convection in microgravitywould alleviate some of the problems of getting these large protein molecules tocrystallise, and indeed that has been the case. Several key proteins of particularinterest to the pharmaceutical industry for drug development have been crystallisedand are under study. In the USA, knowledge of the detailed structure of a protein thatenables the spread of influenza in the body has led to the design of a drug to inhibitits action, with very promising results in cultures and in animals.

Improved European facilities and the opportunities for protein crystal growth on acontinuing basis on the International Space Station will greatly expand the

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generally used in the future, even on manned spacecraft. This is due to the limited timethat the crew has for actual experimental work and the large increase in the amountand complexity of equipment that is due to be flown. Instead the intention is to usethe limited availability of the crew mostly to carry out maintenance work and toprovide for flexible ‘troubleshooting’ activities.

Other than for human-physiology research, the use of a manned spacecraft formicrogravity research has a drawback. That is the disturbance to the microgravityenvironment that occurs as a result of the crew manoeuvring about the spacecraft.Their movement induces an oscillatory response of the spacecraft structure that canimpair the quality of microgravity experiments if these oscillations can couple into thenatural resonance frequency of the experimental equipment. There is also a greaterlikelihood of there being other sources on-board of this higher frequency perturbation,the so-called ‘g-jitter’, due to the fact that manned spacecraft necessarily have agreater amount of moving equipment, which may change the mass distribution. Thisis just one of several potential sources of disturbance to the microgravity environment.

In fact the term ‘microgravity’ itself simply reflects the reality that true weightlessnessor ‘zero gravity’ is a condition that cannot be achieved in a practical system. There arevarious similar effects that induce small gravity-like accelerations in a spacecraft, andalso other external forces that give rise to slowly changing or to transientaccelerations. Thruster firings fall into the latter category. All of these may disturb thebalance of the gravitational and inertial forces, which occurs at the centre of mass ofthe orbiting spacecraft.

The most important perturbation is the frictional drag on the spacecraft, due tocollisions with the thin residual atmosphere at low orbits. This externally acting forcecreates an almost constant deceleration and can also induce a torque, since the centreof pressure and the centre of mass are not coincident. The extent of this atmosphericbraking will vary with the surface area of the spacecraft presented to the incidentparticles of the residual atmosphere. Consequently, changing the orientation of thespacecraft or moveable sections such as solar arrays, will cause a further change tothe microgravity perturbation. A similar effect will occur due to the solar photonradiation pressure.


research are finding application in many industrial and commercial activities, as wellas in human health support. There is certainly no lack of motivation amongst thescientists to develop these research activities further. They look forward to taking fulladvantage of the major new experiment facilities that will become accessible with thecompletion of the International Space Station and the greatly increased time fordetailed experimentation that this will offer.

1.2 Access to Microgravity Conditions

In order to access weightless conditions for long periods of time, it is necessary to gointo space. Only there can the condition of ‘free-fall’, with the gravitational and inertialforces in balance, be sustained over an extended period. Consequently, microgravityexperimentation has made use of a variety of orbiting spacecraft since its inception.Mostly these have been manned and have used the crew as an essential part of theexperimentation as operators. The crew have also been used as the test subjects inhuman-physiology studies. Whilst this latter aspect has been very valuable, therestricted number of crew members and their closely defined physiological conditionhas also limited the extent of and the statistical base for such studies.

Automation of microgravity experiments is generally possible and can be successfullyimplemented, provided that the data-transmission capabilities to and from Earth aresufficient to permit real-time control of the experiment situation from the ground. Thistype of remote experiment operation, termed ‘telescience’, is likely to become more

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Figure 1.1. The quality of microgravity conditions and their duration for various flightopportunities Figure 1.2. The quasi-static microgravity-level contours for the International Space Station (ISS)

Parabolic Flights typically provide 20–30 seconds of low-gravity conditions. They usea jet aircraft with the interior specially fitted out to accommodate experiments. Anaccelerating entry flight is followed by a pull up and engine throttle back, to allow theaircraft to free-fly a parabolic trajectory. After leaving the free-fall parabolic trajectory,there is a short horizontal flight phase and then successive parabolic manoeuvres areagain possible. These flights are particularly valuable for astronaut training and for thetesting of experiment equipment and operating methodologies. Their limitation is thepoor level of microgravity achieved over just a short duration.

Sounding Rockets were one of the earliest means of achieving microgravity conditions.They too use a parabolic free-flying trajectory, but the microgravity conditions aremuch better than for the parabolic airplane flights. European flights (Texus) havefrequently used the Skylark rocket, originally providing about 6 minutes of free-fallconditions. In addition, the Maxus sounding rocket now provides about 13 minutes ofmicrogravity and can take a scientific payload mass of around 450 kg. Within thelimited time frames and the need for largely independent operations, it is possible tocarry out valuable experiments with these latest systems.

Space Platforms and Capsules potentially offer very low microgravity levels, sincethey are entirely free from any perturbations due to launch vehicles. They are injectedinto orbit and have a useful lifetime for experimentation that is limited only by theavailability of any required consumables and the natural decay time from orbit due toatmospheric drag.

The Russian Bion/Foton capsule has been regularly used for microgravity experimentsin Europe. This capsule can accommodate a maximum scientific payload of 500 kg


Since it is obviously impossible to locate all of the microgravity experiments preciselyat the spacecraft’s centre of mass, where there is exact equilibrium between thegravitational and centrifugal forces, it follows that there will be an unbalanced ‘tidal’force acting on equipment at other locations. The resulting perturbing acceleration willdegrade the microgravity conditions, as illustrated in Figure 1.2 for the ISS. The extentof that degradation depends upon the geometrical relationship between theequipment, the centre of mass and the gravity vector. It may therefore also vary duringan orbital period, in a manner that depends upon the flight orientation of thespacecraft during its movement through the orbit.

Access to the best microgravity conditions is therefore a matter of careful siting of theequipment, operating it during times of limited transient disturbances and, for thevery best conditions, taking steps to isolate the experiment from transientperturbations. This may be done simply, by decoupling the experiment from thespacecraft structure using spring/damping elements. A more sophisticatedarrangement would be damping actuators controlled by acceleration sensors. For asmall element of an experiment, a levitation system might also be feasible.

The accompanying table shows some of the types of systems and spacecraft that havebeen or will be used to provide access to microgravity experimentation. The indicatedmicrogravity levels point to the superiority of unmanned vehicles for the lowest levelof disturbances. The figures for the Space Station elements include provision for free-floating experiments, in order to achieve the least microgravity disturbance.

Drop Towers are usually evacuated tubes in which an experiment capsule is releasedand allowed to free-fall. Several countries have such facilities. The one in Bremen(ZARM) is typical and provides a 110 metre drop and about 5 seconds of microgravityconditions. They are of value for short-duration self-contained experiments, such asphase flow, combustion and capillarity, and for testing experiments destined for longerduration missions.

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Flight Facility Microgravity Level Microgravity Payload Mass Duration (kg)

Drop Tower < 10 –5 g 5 seconds 125Parabolic Aircraft Flight 10 –2 20 – 30 seconds 50 *Sounding Rocket (Maxus) 10 –4 2 –15 minutes 450Retrievable Capsules (Foton/Bion) 10 –5 16 days 500Shuttle Pallet Satellite (SPAS) 10 –6 2 days < 900Spacelab < 10 –4 10 – 14 days 4500 Eureca 10 –5 11 months 1000ISS/Columbus Laboratory 10 –3 to 10 –6 * Years 4000*Free-floating experiments

Figure 1.3. (a) Schematic of the parabolic-flight manoeuvre leading to low-gravityconditions, and (b) the result on an ESAparabolic flight in October 1994 asscientists perform fluid measurements(courtesy of S. Odenbach, Univ. Wuppertal,and J. Fabre, IMFT, Toulouse)

(a)

(b)

intervention in the case of problems, provides for operational flexibility and cansimplify experiment design.

Spacelab was developed by ESA as a manned laboratory, to be accommodated in thecargo bay of NASA’s re-usable Space Shuttle. Both Spacelab and Eureca wereconstructed during the same time period, as an agreed parallel undertaking.

The pressurised section of Spacelab is about 6 m long and 4 m in diameter, but themodular construction provides for flexibility in the actual flight configuration. In theLong-Module configuration, which maximises the accommodation for internalpayloads, it can accommodate a mixture of 10 double racks for equipment (112 cmwidth) and 4 single racks, with a total payload mass of about 4500 kg. Up to seven crew members can be carried, several of whom have scientific training andcompetence in the experiment subject. Mission duration is nominally 10 days. Up tofive external pallets, each 2.9 m long, can provide accommodation to a variety ofpayloads. With a Three-Pallet configuration, a total mass of 9300 kg may be carried.

Spacelab has been the workhorse of microgravity science for about 15 years. Itprovides substantial crew support to experiments and as subjects for humanphysiology studies. The overall resources are adequate and the microgravity levels areacceptable for most experiments. The problem has been the infrequent flightopportunities for many scientists, coupled with a short mission duration. The resulthas been a difficulty in rapidly following up on interesting observations. It has alsobeen difficult, in some cases, to establish a sufficient body of data by the normalprocess of careful checks using several subjects or samples. Nonetheless, it may bejudged to have been very successful at providing extensive, flexible, high-qualityaccess to microgravity conditions for a generation of scientists.

Spacehab is a commercial development of a pressurised module that is also designedto fit into the Shuttle’s cargo bay. The module has a volume of 31 m3 and can beconnected into the Shuttle. It is more limited in its capabilities than Spacelab, but ithas a shorter turn-around time between flights and it is cheaper to operate.Consequently, Spacehab is being used now as a manned laboratory for microgravityexperiments, having first flown in 1993.

Mir was the first true space station, following on from the limited orbital stations ofSalyut-1 in 1971 and Skylab in 1973. Assembly of Mir was begun in orbit in 1986 bythe Soviet Union. It survived the political changes of the following decade, continuingto operate and carry out a variety of scientific research. Assembly was finallycompleted in 1996. By that time, it had become international in the extent of its use,although still owned and operated by the Russian Space Agency. The maincharacteristics and functions of Mir are summarised in the accompanying table.


and can be launched into an orbit of up to 400 km altitude. Experiments can beperformed over a period of up to 16 days. On completion of the experiment phase, aretrothrust is activated to cause descent and re-entry. ESA has used the Foton systemto fly and return the Biobox and Biopan biology research payloads and the Fluidpacfacility.

SPAS, the German Shuttle Pallet Satellite, can be launched into orbit and laterrecovered by the NASA Shuttle. It carries up to 900 kg of payload and has sufficientresources to permit microgravity experimentation over a period of two days. Theprincipal limitation on in-orbit operations is the lack of solar arrays and hence adependence on battery power. The advantage is that with the absence of arrays theatmospheric drag is much lower and very low microgravity levels are achievable. Ithas been flown several times since its first launch in 1983, although with limited usefor microgravity payloads.

Eureca, the European Retrievable Carrier, was designed by ESA as a long-durationautomated microgravity platform. It was launched in August 1992 and recovered inJuly 1993, by the NASA Shuttle. It had an experiment payload capacity of 1000 kg. Thehigh potential re-flight costs caused cancellation of the programme. Despite the goodmicrogravity environment on this platform, the preference appeared to be to usemanned vehicles for large experiment operations. This opens up the possibility of crew

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Figure 1.4. Spacelab in theShuttle’s Cargo Bay and the firstShuttle/Spacelab launch, on 28 November 1983

The International Space Station is already being assembled in orbit. It promises toherald a new era in microgravity research by virtue of the amount and diversity ofexperimental equipment that is accommodated for this purpose and the extendedtime during which it can be used.

At completion, the Station will have a total mass of over 400 tons and dimensions ofabout 100 metres by 75 metres. Out of the total power of 110 kW, some 47 kW will bemade available for research purposes. Initially, there will be three astronauts on board,increasing to around six at final assembly. Each astronaut will remain on the Stationfor at least three months, corresponding to the time interval between normal Shuttlere-supply flights.

There will be six pressurised laboratories attached to the Station: one from the USA,one from Japan and one from ESA, plus two from Russia and a US centrifuge module.Several unpressurised accommodation sites will also be available for scientificequipment, serviced by remote manipulator arms.

Inside each of the pressurised laboratories there will be standard experimentequipment racks, each fitted with in-situ resource provisions for the experiments. Inthe case of the ESA research module, the ‘Columbus Laboratory’, there will be tenexchangeable payload racks, i.e. four along each side and two in the ceiling of the 6.7 m by 4.5 m diameter module. The mass of this Laboratory and its equipment willbe about 15 tons, 5 tons of which will be research equipment. Five of the ten racks willbe available for ESA research, and five for NASA research. Much of the experiment


Mir was initially somewhat constrained in its research capabilities, mainly by the lackof adequate data-handling and communications capabilities. That limitation waspartly overcome by emphasising research that used returned samples. These wereprincipally concerned with life sciences and improving the properties of materialssuch as semiconductors, alloy systems, optical and sensor materials. The researchactivities were expanded and the quality of the facilities for microgravity research wasimproved, as the partnership with the USA in the operations got underway.

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Module Mass Length Max. Pressurised Electrical Function(tons) (m) Diameter (m) Volume (m3) Power (kW)

Mir Core 21 13 4.15 90 10 Habit./ Support Syst.

Kvant-1 11 5.8 4.15 40 - Astrophys.Kvant-2 18.5 12.4 4.35 61 7 Earth Obs.Kristall 19.6 12 4.35 61 5 – 8 Mat. ScienceSpektr 19.6 12 4.35 62 7 Geophys.Priroda 19.7 12 4.35 66 - Earth Obs.,

Geophys.

Figure 1.5. The Mir space station in its final configuration

Figure 1.6. The International Space Station (ISS)

shown in the accompanying illustration, the re-boost process is combined into thetime frame for the re-supply rendezvous, when further major disturbances occur. Theresult is that acceptable microgravity conditions for experimentation are availableonly in discrete periods of 80 days. That is still extremely long compared to what waspreviously available, but it will circumscribe a few experiments.

Clearly, with the advent of full operations on the ISS, scientists will have far greateraccess to microgravity conditions than was ever previously possible. But to use thataccess effectively, they will have to adapt to a new way of experimenting. They willhave to bypass potential bottlenecks in research operations due to communications,crew-time and supply-logistics limitations. That means designing experiments andprocedures to new levels of automation that include local intelligence and control. Itmeans using in-situ analysis wherever possible, limiting the total mass of specimensneeded and the quantity of consumable materials in experiments. Finally, they willhave to ensure that experiment equipment is robust and easily maintained, since it islikely to be used in-orbit for an extended time and both crew time and spares provisionare going to be restricted.

1.3 European Manned Spaceflight and Microgravity Research

July 1969 saw one of the most spectacular events in technological history, thelegendary human landing on the Moon. With this extraordinary achievement theUnited States surpassed the Soviet Union, which had thus far led the space race withthe launch of the first artificial satellite ‘Sputnik’ on 4 October 1957 and with the flightof the first man, Yuri Gagarin, in an Earth orbit on 12 April 1961.


equipment within the pressurised module will be dedicated to microgravity research.Payloads will also be attached on four external pallets on the exterior of the ColumbusLaboratory for technology experiments, Earth observation and space-scienceinvestigations.

The resources allocated to support the operation of the five payload racks ofequipment, available in the Columbus Laboratory for European scientists, and theexternal pallet payloads, amount to an average of 2.5 kW of power and just over13 hours/week of crew time. Within that limited crew-time allocation is therequirement for experiment equipment maintenance as well as assistance toexperiment operations.

It is here and in the data-transmission resource allocation that scientists mayencounter limitations to what they can achieve, despite the huge amount ofequipment that is potentially available for their use. In that sense, the conditions thatwere available in the Spacelab, with a similar number of crew available for fewer racksof equipment, no maintenance, ample resources, and good data links, may seem aluxury. The major disadvantage with the Spacelab is, however, the more serious one offew flights and each of short duration.

Another limit to experiments in the ISS is set by the need to periodically boost theStation back into its original orbit, following the natural orbital decay due toatmospheric drag. At that time, the microgravity conditions are greatly disturbed. As

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Figure 1.7. ESA’s ISS Columbus Laboratory

Figure 1.8. A basic plan for the ISS re-supply, orbit boost and experiment cycles

The decision to develop Spacelab was part of an overall agreement within Europe thatalso included a decision to develop a European launcher system (later named ‘Ariane’),and a series of telecommunication satellites. These three elements, together with thecontinuation of the Space Science Programme of the original ESRO, were to form thecore activities of the new European Space Agency (ESA).

For Europe, the introduction of the Spacelab Programme opened the way to start thenovel scientific and application oriented microgravity research activities. It led to theformation of a new scientific community, consisting of life, materials, and fluidscientists, which started to explore the potential of the microgravity environment andthe use of gravity as a variable.

Although in the original programme decision the multidisciplinary character ofSpacelab was stressed, it soon became clear that this new infrastructure would largelybe used for microgravity research. The accompanying table of Spacelab missions,which terminated in 1998 with the Neurolab mission, confirms this prediction.

The Shuttle/Spacelab system operated in the period from November 1983 to April1998, providing 16 missions with the Spacelab Long Module (LM), 13 of which werededicated to life sciences and/or materials/fluid sciences (MS/FS). The other three LMmissions – the joint NASA/ESA SL-1 mission in 1983, and the two German Spacelabmissions (D-1 in 1985 and D-2 in 1993) – were multi-disciplinary, but had more thanhalf of their payloads dedicated to the microgravity research disciplines. In addition,on 16 further Shuttle missions Spacelab unpressurised pallets were flown. NASA flewa materials-science pallet on several of these missions.

The Shuttle/Spacelab combination, with the pressurised Long Module and a spacemission of 1–2 weeks, represented a rather ideal research opportunity for themicrogravity disciplines. The limitation, from a European perspective, lay in the verylimited flight opportunities. This had its origins in the early gross underestimation byNASA of the Shuttle maintenance and turn-around complexity and of the associatedflight and operations costs. This was presented as $18 million/flight in the 1975 plans.By 1990 it stood at $220 million and in 1999 it was $500 million. Instead of the 50 flightsper year originally assumed as feasible in 1975, only 8 per year were routinely achieved.

The result of the escalating flight costs was that the ESA Member States were unwillingto fund ESA Spacelab missions, after the initial joint NASA/ESA SL-1 mission. ESA haddetailed plans prepared in the late 1970s for two Shuttle/Spacelab missions, but noconsensus could be found among Member States to finance them. Therefore Germany,which had already financed more than 50% of the Spacelab development costs withinthe framework of the ESA programme, performed two German national missions (D-1in 1985 and D-2 in 1993). In so doing, it agreed to a minority participation of ESAscientific payloads in those missions.


The launch of the Sputnik satellite shocked the USA out of its complacency regardingits technical superiority. NASA was then created in 1958, as part of the rush to recoverthe initiative. In 1960, President Kennedy announced that it was an American nationalobjective to land an American on the Moon before 1970, in the framework of NASA’sApollo Programme. With the successful accomplishment of that declared objective in1969, the USA again demonstrated their superiority in high technology and confirmedtheir lead in the space race with the Soviet Union.

The West European nations had by then already begun the process of combining theireconomic forces in the form of the European Economic Community, which thenrepresented the second largest economic power in the world. Despite that fact, Europedid not play any role in this demonstration of technical leadership. Consequently, adesire was created in Europe to participate in the next steps in the mannedexploration of space.

The European Space Research Organisation (ESRO) had been created and built upduring the mid-1960s in order to expand European capabilities in space science. Witha progressive expansion of its activities and capabilities, it was in a position by 1973to accept an invitation from NASA to participate in an international Post-ApolloProgramme. This important decision marked the beginning of the manned-spaceflightprogramme within Europe and it led to the transformation of ESRO into a full EuropeanSpace Agency.

The Post-Apollo Programme at that stage contained several options for the wayforward, including a possible Space Station. However, the NASA-selected option for thePost-Apollo Programme, announced in 1972, was the Space Transportation System(STS), involving the development of the Space Shuttle. The development of a SpaceStation as an alternative was postponed.

The subsequent joint European–American selection of Spacelab as the Europeanelement of the STS was mainly due to US national security concerns about overlappingtechnology developments, and to the European desire to develop an easily identifiableelement of the STS that could be built independently by European industry. Spacelabwas to be the first manned multi-disciplinary research laboratory to be routinely usedin space, and the concept fulfilled both the European aspirations and the Americanrequirements.

Two Spacelab flight units and an engineering model were finally delivered by ESA toNASA, for launch and orbital operation by NASA. However, due to delays in the Shuttleand Spacelab development, the first Shuttle/Spacelab mission, SL-1, did not take placeuntil 28 November 1983, with a 10-day mission. Ulf Merbold was aboard, as the firstESA and non-American Shuttle astronaut.

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In January 1982, the ESA Member States finally agreed to a small programme to whichgovernments could contribute according to their interests and their budget. The ESAMicrogravity Programme: Phase-1 for 1982-85 amounted to 48 million ECU. Thisallowed ESA to participate in the German ‘Texus’ Sounding-Rocket Programme, and toextend it by the inclusion of the Swedish Maser Sounding Rockets (withpredominantly ESA payloads) to perform short-duration microgravity experiments. Inaddition, this Phase-1 programme covered the development of a first set of multi-userexperiment facilities for Spacelab missions.

With the approval of a larger budget for Phase-2 of the ESA Microgravity Programmein early 1985 (later twice extended and named EMIR-1, European MicrogravityResearch Programme), ESA was in a position to establish bilateral co-operation withboth the Life Sciences Office and the Materials and Fluid Sciences Office of NASA.

Unfortunately, during this period when microgravity research was beginning toaccelerate, the tragic Challenger accident occurred on 28 January 1986, which led toan interruption of Shuttle/Spacelab missions for more than five years. During thatperiod, attention was focused upon alternative means of accessing microgravityconditions and the sounding rockets provided an important element of this.

Within the framework of the co-operation between the ESA and the NASA microgravityscience offices, an agreement was developed for joint (50/50) NASA/ESA use of abouta dozen multi-user experimental facilities. These were to be ESA-funded and built byEuropean industry. NASA agreed to cover the cost of the flights and the orbitaloperations of these facilities on Shuttle/Spacelab missions.

These ESA facilities were required to carry out novel microgravity experiments withinSpacelab. They were at the forefront of high-technology equipment and had a highpotential for future applications and ‘spin-offs’.

With this very favourable arrangement for European scientists at a critical time, theseESA multi-user facilities flew on five NASA Shuttle/Spacelab missions: – 1992 on the IML-1 (International Microgravity Laboratory 1) mission– 1994 on the IML-2 mission– 1995 on the USML-2 (US Microgravity Laboratory) mission– 1996 on the LMS (Life and Microgravity Sciences) mission– 1998 on the Neurolab Spacelab mission, dedicated to neurophysiology.

A similar arrangement (with a small ESA contribution for the Shuttle launch costs) wasalso made with the German space authorities. It led to ESA’s participation with multi-user facilities in the German national Spacelab missions D-1 in 1985 and D-2 in 1993.In total, this meant that ESA participated in eight of the 16 Shuttle/Spacelab missionsin which the Spacelab Long Module Laboratory was flown.

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Spacelab Missions using the Long-Module (Laboratory) Configuration

STS-Flight Spacelab Launch Orbit Research European ESA Number/ Mission Date + Inclination/ Discipline Astronaut Participation

Duration Altitude with Payload

STS-9 SL-01 28-11-83 57º Multi- U. Merbold 50%Columbia FSLP 10 days 250 km Disciplinary

STS-17 SL-03 29-04-85 57º Mat./Fluid – –Challenger 7 days 360 km Sciences

STS-22 SL-D1 30-10-85 57º Mat./Fluid R. Furrer 38%Challenger 7 days 330 km Science + E. Messerschmid

Life Sciences W. Ockels

STS-40 SLS-01 05-06-91 39º Life Sciences – –Columbia 9 days 300 km

STS-42 IML-01 22-01-92 57º Mat./Fluid U. Merbold 25 %Discovery 8 days 300 km Science +

Life Sciences

STS-50 USML-01 25-06-92 28º Mat./Fluid – –Columbia 14 days 300 km Sciences

STS-47 SL-J 12-09-92 57º Mat./Fluid – JapaneseEndeavour 8 days 300 km Sci.+ Life Sci. Payload

STS-55 SL-D2 26-04-93 28º Multi- M. Schlegel 25 %Columbia 10 days 300 km Disciplinary U. Walter

STS-58 SLS-02 18-10-93 39º Life Sciences –Columbia 14 days 280 km

STS-65 IML-02 08-07-94 28º Mat./Fluid – 35%Columbia 15 days 300 km Science +

Life Sciences

STS-71 SL-M 27-06-95 52º Mission to – –Atlantis 10 days 300 km Mir

STS-73 USML-02 20-10-95 39º Mat./Fluid – 10 %Columbia 16 days 300 km Sciences

STS-78 LMS 20-06-96 39º Mat./Fluid J.J. Favier 35 %Columbia 17 days 280 km Science +

Life Science

STS-83 MSL-01 04-04-97 28º Mat./Fluid – ESA MGColumbia 4 days 300 km Sciences Measurement

Ass.

STS-94 MSL-01R 01-07-97 28º Mat./Fluid – ESA MGColumbia Refl. of 16 days 300 km Sciences Measurement

STS-83 Ass.

STS-90 Neurolab 17-04-98 28º Life Sciences – 25 %Columbia 16 days 300 km

ESA also extended the experimental opportunities for human physiology by reachingan agreement with the Russian Space Agency to perform, on a cost-reimbursablebasis, two missions to Mir carrying an ESA astronaut on each one. These were:– Euromir ’94, 30-day mission, astronaut Ulf Merbold– Euromir ’95, 179-day mission, astronaut Thomas Reiter.

Although these missions were successfully performed, the experimentation on Mirwas constrained by the very low download of only 10–15 kg for experimentalequipment and specimens and by the low capability of the data downlink.

The Spacelab era was drawing to a close, as planned, in the mid-1990s, yet theassembly of the International Space Station had not begun. To fill the resulting gap, areplacement of Spacelab missions by those of a smaller commercial space laboratory,called ‘Spacehab’, was therefore offered by the American company, Spacehab Inc.Spacehab utilisation by ESA started in June 1993, with the first flight of ESA’sAdvanced Protein Crystallisation Facility (APCF) on Spacehab’s maiden flight.Spacehab utilisation was continued in 1996 with several NASA/ESA co-operative (nomission costs for ESA) flights of the ESA Biorack multi-user facility. ESA has used theseSpacehab flight opportunities since 1998 also on a commercial basis, flying just a fewexperimental facilities (multi-user and experiment dedicated ones).

During the eight Spacelab missions in which ESA microgravity scientists haveparticipated, with a total mission duration of slightly more than 100 days, theexperimentation time was about 2500 hours. This was spread over the 15-yearduration of the Spacelab era. Despite the constraints on experimentation time thatthis implies, European scientists have achieved very substantial research results. Theyhave made a number of unexpected discoveries, have acquired outstanding expertisein performing their experiments in space, and in several microgravity subdisciplineshave taken a worldwide lead.

During the 15 years of the Spacelab era (1983–1998), astronauts from 20 differentcountries have performed experiments from European, American, Japanese andCanadian investigators in Spacelab.

Within the framework of the STS-84 mission in May 1997, Spacelab was even used ina Shuttle flight to the Russian Space Station Mir. This mission was part of Phase-1 ofthe worldwide co-operation that was established in order to gain experience for theconstruction and operation of the International Space Station (ISS).

- The Space Station and Microgravity

Europe needed more than 10 years to decide on the extent of its participation in theISS, with the final decision being taken at the ESA Council at Ministerial Level in 1995.


Some of the European materials and fluid scientists had requested better microgravitylevels than were achievable on Spacelab missions. There were also requests from theEuropean life scientists working in the field of radiation health/exobiology for longermission durations. Consequently, ESA decided to develop a large (5 ton) retrievablecarrier platform called Eureca (European Retrievable Carrier). This was launched by theShuttle on 1 August 1992 and retrieved by it after 11 months of free flight in a 400 kmaltitude circular orbit. Eureca yielded the lowest microgravity levels yet obtained,together with some good scientific results. Nonetheless, it was not possible to find thefunding for a reflight from within the ESA Member States.

In order to expand the Europeanmicrogravity research opportunitiesfurther, ESA provided an improvement toits Sounding Rocket Programme in 1993by promoting an industrial initiative for alarger rocket, the Maxus. It providesgood microgravity levels for about 13 minutes of flight (double that of theTexus and Maser missions) and has apayload-carrying capability of up to 450 kg, compared to the Texus/Masercapacity of 240 kg.

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Figure 1.9. Eureca in its operational orbit(courtesy of Astrium/DASA)

Figure 1.10. Mission profiles of the Mini-Texus, Texus, and Maxus sounding rockets(courtesy of Astrium/DASA)

Furthermore, ESA is participating actively in the ISS Ground Segment, providing theControl Centres for both the Columbus Laboratory and the ATV operations.

ESA’s ISS Utilisation Preparation Programme was established in order to:– develop Laboratory Support Equipment (LSE) for the ISS laboratories – familiarise the user community with ISS– prepare for the orbital operations, including the selection and training of astronauts.

The ISS provides the following utilisation characteristics:– regular and permanent access for a period of 15 years– permanent manned capability, i.e. the crew is exchanged at regular intervals (every

3 months)– large technical resources, such as electrical energy, heat rejection and data

transmission, are provided for research in the various pressurised laboratories andat the external viewing sites of the ISS.

These characteristics will radically change the microgravity utilisation of the low-Earthorbit, from a situation where Spacelab flights were too few and sporadic, to a stableand continuous utilisation mode on the ISS.

In anticipation of the utilisation of the ISS by the microgravity disciplines, ESA hasstarted to extend its scientific user community through a complementary MicrogravityApplication Promotion (MAP) Programme. The latter, presently financed by theUtilisation Promotion Element of the Columbus Programme, covers two types ofactivities: Topical Teams (TTs), and pilot research projects called ‘MAP Projects’. TheTTs are European teams from academia and industry, which have the task of defininghigh-priority research areas with special relevance to microgravity. Based upon the recommendations of these Teams, MAP Projects are carried out by integratedteams composed of scientists from universities and also researchers from industry.They undertake relevant ground-based research and eventually space research, inorder to obtain data for the optimisation of industrial processing and medical applicationson Earth.

Taking into account the permanent access opportunities to the space laboratories ofthe ISS, these MAP teams will perform applied research programmes in a similar wayto those in a normal terrestrial laboratory. The limitations due to the sporadic isolatedexperiments of the previous era, which have severely circumscribed microgravityresearch in the past, will finally be overcome. The topics addressed will have thepotential to develop into concrete industrial and health-related applications on Earth(see Sections 3.3 and 5.1).

ESA provides financial support for the academic partners of the MAP Projects, whereasthe industrial MAP partners contribute in cash and/or in kind. ESA takes care of the


The ISS assembly phase started in late 1998, with the launch of the Russian module‘Zarya’ and the American ‘Unity’ module. This assembly process will last until 2005,at which point the routine utilisation of the ISS will start.

ISS is the largest space programme ever undertaken. With the decision by Russia toaccept the USA’s invitation to become a partner in ISS in January 1998, all of theworld’s major space powers concentrated their efforts on this ISS programme. Thepermanently manned ISS will demonstrate visibly to the world the advanced technicalknow-how of the ISS partners. In addition, the ISS has become the largest East-Westcooperation. It offers the chance to create mutual confidence and at the same timeillustrates how political and cultural obstacles can be overcome in a joint enterprise.

Besides these positive political aspects, the ISS programme is designed to provide ascientific and technical research platform above the Earth’s atmosphere, with the aimof contributing (thanks to its particular position in low-Earth orbit) towards solvingproblems on Earth and in the Earth’s atmosphere, and of acceleratingscientific/technical progress.

The principal responsibilities, tasks and rights of each of the five ISS Partners, i.e. of theUSA, Russia, Japan, Canada and Europe, were agreed already in 1988 in theIntergovernmental Agreement (IGA), in which the five Partners delegate themanagement of ISS to their respective space agencies. In Europe, ESA represents the10 ESA Member States that finance the European ISS contribution.

In addition, the four ISS partner agencies of NASA concluded bi-lateral Memoranda ofUnderstanding (MOUs) with it, which define the detailed responsibilities, managementstructures and mechanisms, the attribution of installations and resources and thesharing of the costs.

The European participation in the ISS consists of three major elements, representing8.3% of the (non-Russian part of) ISS. These are the:– contribution of the pressurised Columbus Laboratory with an attached external

platform– participation, with Ariane-5 and the Automated Transfer Vehicle (ATV), in the logistics

flights to the ISS– ISS Utilisation Preparation Programme.

In addition to these three major programme elements, ESA is making several other keycontributions to the ISS, including:– the European Robotic Arm (ERA), for the Russian segment of the ISS– the Data Management System for the Russian Service Module ‘Zvezda’, launched on

12 July 2000– in co-operation with NASA, the Crew Re-entry Vehicle (CRV).

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space transportation and of the development of the major experimental facilitiesneeded by the MAPs.

By the end of 2000, some 44 MAP Projects had already been established, representinga financial envelope of about 40 MEuro. ESA contributes one third of this envelope,and the other two-thirds are covered by industry and the research institutes of theacademic MAP members.

Overall, the annual financial resources that Member States have made available for theoptional ESA Microgravity Programme, in the period 1982 – 2000, were in the rangeof 0.5% to 3% of the ESA annual budget. The research results obtained, which arediscussed in detail in the following Chapter, demonstrate how well and how cost-effectively these modest resources have been used.

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CHAPTER 2. ASPECTS OF CURRENTMICROGRAVITY RESEARCH

2.1 CHANGES TO HUMAN PHYSIOLOGY INSPACE, AND SPACE MEDICINE

2.1.1. The Cardiovascular System

K. Kirsch & H-C. Gunga

2.1.1.1 Introduction

In the mid-seventies, when the Europeans started to participate actively in theAmerican space programme aboard the Space Shuttle, they had no biomedical space-research experience of their own, relying for all practical issues on the Americans.NASA, on the other hand, could already look back on their Gemini experiments of thesixties and, particularly, the longer highly successful Skylab missions of the earlyseventies. The results from the latter are well-documented and in many ways shapedthe thinking and planning for the early Shuttle missions.

This does not mean that Europe totally lacked experience in gravitational physiology.During the 1930s and 1940s, centrifuge experiments had been conducted andtherefore there were hypergravity physiology data available. Using these data, Gauerand Haber extrapolated from hypergravity to 0g, making certain predictions about theeffects of a microgravity environment on the human body. The cardiovascular systemwas identified as a possible problem area, since it was known from the centrifugeexperiments that gravity strongly influences the distribution of blood within thehuman body.

Knowledge was also acquired from certain aspects of developmental and comparativephysiology. When aquatic animals left their home environment, for example, theywere fully exposed to the forces of gravity and the weight of their bodies impededmovement. Evolutionary processes had to ‘produce’ the structures to overcome theburden induced by gravity. Height only became an exploitable dimension when thebody developed the necessary supporting muscles and bones. These maintain and


Should fluids leak out of the blood vessels, they accumulate within the tissues of thelegs, producing oedema. The body therefore has had to develop oedema-preventingmechanisms, which are just one of the many mechanisms used by the cardiovascularsystem to counteract gravity. In the supine position, these problems are of littleimportance. For worms or snails crawling on the ground, therefore, gravity plays onlya minor role (Fig. 2.1.1.1, right).

In Figure 2.1.1.2, the cardiovascular system of long-necked animals like the giraffe andthe dinosaur is compared with that of man. The problem is obvious: the giraffe’s heartis some 2.4 m above the ground and the distance from the heart to the brain is 2.8 m.For the dinosaur, these distances are 3.8 and 7.9 m, respectively. Long hydrostatic fluidcolumns are therefore present. The giraffe’s heart, for example, has to create a bloodpressure of almost 400 mm Hg to ensure an adequate perfusion pressure for the brain(Fig. 2.1.1.3). The dinosaur’s heart would have needed to generate a pressure of almost800 mm Hg. Below heart level, the hydrostatic pressure has to be added to the heart-generated pressure. The arterial pressure in the dinosaur’s limbs must therefore havebeen more than one atmosphere. Man’s blood pressure is typically around 120 mmHg and seldom exceeds 180 mm Hg, even during exercise. Clearly, gravity sets criticallimits for these tall animals.

One might argue that by man assuming a supine position, as in bed rest, manyproblems would be solved. This is not the case, however, because a healthy and activeperson spends about two-thirds of their day on their feet or haunches, and when in asupine position a de-conditioning process sets in very rapidly, reducing their ability towithstand the stress of standing upright (orthostasis). Even the 30 cm from heart tobrain then becomes a problem and fainting is common upon standing after extendedbed rest. Consequently, bed rest is often used to simulate the type of de-conditioningseen in astronauts after their return from space.

Ageing and upright posture may also be considered from a gravitational viewpoint.Man’s upright posture is an everlasting struggle against gravity. A newborn baby, for


support the unstable assemblage of fluid-filled bags and interconnected tubesdirected along the body axis, whichroughly approximate to the cardiovascularsystem in man and animals. Within thesetubes, there are hydrostatic forces at workthat have to be counteracted if thecreatures are to survive.

These problems are illustrated in Figure2.1.1.1, showing the human cardio-vascular system, and Figure 2.1.1.2, whichshows that of a giraffe and a dinosaur.

The human cardiovascular system isunique, in that the heart is 1.4 – 1.5 mabove the ground, while the brain sits ontop of the whole structure and needs to becontinuously perfused by blood. The hearthas to overcome a height difference to thehead of 30 to 35 cm in the standingposition. In the organs that lie below the heart, blood tends to accumulate and needsto be transported back to the heart, also against the forces of gravity. Bearing in mindthat about 70% of the total blood volume is located below the heart, this is a majortask.

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Figure 2.1.1.1. The human cardiovascularsystem. Note the position of the heart inrelation to the feet and the brain. Thesystem consists of long verticallyorganised tubes, in which highhydrostatic pressures can occur. This canbe compared (right) with the horizontallyorganised vascular system of the worm orsnail

Figure 2.1.1.2. Schematic of the major hydrostatic distances acting on the heart and fromcirculatory systems in man, in the giraffe, and in the dinosaur Brachiosaurus branci(Gunga et al.1999, Mitt. Mus. Nat. Berl. Geowiss., p. 97)

Figure 2.1.1.3. The arterial blood pressures of man and giraffe

The most dramatic changes can be expected in the early mission phases, particularlyin the vestibular (see Section 2.1.6) and electrolyte control (see Section 2.1.3) systems.What is seen in space therefore often depends upon when during the mission theexperiments are performed (Fig. 2.1.1.4).

Figure 2.1.1.4 shows that the changes in the fluid and electrolyte systems occur ratherearly in the mission, with astronauts losing between 4 and 8% of their body weight inthe first week of a mission, due mostly to water loss from extra-cellular fluid space. Theblood volume shrinks accordingly in a process that influences cardiovascularfunctions. After 1.5 months, a new equilibrium is reached, known as the ‘0g set point’.The cardiovascular system reacts more slowly, showing the widest deviations from the1g and the 0g set point after two to three weeks in space. Later, many of the systemsreach a new equilibrium, allowing them to cope with the demands of this foreignenvironment. What, then, do these adjustments to microgravity mean when theastronauts return to Earth?

- Hypotheses from Terrestrial Experiments

Terrestrial simulation experiments, such as bed-rest, head-down-tilt and immersionstudies, attempt to remove the head-to-foot gravity vector or to shift blood from thelower parts of the body towards the cephalic areas. The latter can be accomplishedbest by water immersion, as demonstrated in Figure 2.1.1.5.

Standing upright induces the accumulation of blood and fluid in the lower parts of thebody, as seen on the left (A). Standing in water (B,C) leads to fluid accumulation withinthe intra-thoracic circulation zones, because the hydrostatic pressure acts on the


example, is unable to stand. Neither the skeletal-muscle nor the cardiovascular systemis sufficiently developed. It takes about two years for an infant to be capable ofcontrolled movement in an upright position. The small arteries of the cardiovascularsystem, the arterioles in the lower limbs, have to develop constricting muscles withintheir walls to withstand the hydrostatic forces when standing. This is a matter oftraining in the Earth’s gravity. This is even more the case for the venous system, inwhich the volume holding capacity is always challenged by gravity.

Removing the gravitational forces from these structures by entering the microgravityconditions of space leads to progressive wasting of the muscles in the blood vessels.Consequently, returning to Earth and normal gravitation leads to widening of thevessels of the lower limbs and increased blood pooling. Insufficient blood thenremains in the heart and lungs, cardiac output is reduced and brain perfusion isendangered. Fainting tends to ensue, as is often observed in astronauts returning froma lengthy space flight.

In the course of maturing, man develops heavy ‘antigravity muscles’ around his hipsand legs, which are constantly at work to prevent falling, whereby they also pumpblood back towards the heart. A conservative estimate is that 50% of muscle masscan be regarded as antigravity muscles, which must be adequately perfused tosupport an upright gait.

After the age of about 40, wasting of the antigravity muscles becomes apparent andthe cardiovascular system also starts to deteriorate. As these processes progress,there is an increasing tendency to seek the support of a chair, for instance, to obtainrelief in the fight against gravity. The walking stick, and later the wheelchair, may markthe eventual triumph of gravity over a wasting musculature and degeneratingcardiovascular system. It therefore came as no surprise that gravity’s removal wouldhave a major impact on practically all of the human body’s systems, and thecardiovascular system in particular.

2.1.1.2 The Cardiovascular System in Space

- Operational Demands

From what has already been said, one could expect dramatic changes in man’scardiovascular system on entering a microgravity environment. The observations thatwere made, and the data finally obtained, depended upon the circumstancesprevailing during a particular space mission. The experimental approach in space isoften dictated by the operational demands of the mission and by the methodologicalpossibilities available. Any measuring equipment needs to be easy to handle for theastronauts and the experiments should not be too time-consuming, so that as manyas possible can be performed in the time available.

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Figure 2.1.1.4. The course of physiological acclimatisation to weightless conditions

- Fluid-Shift Mechanisms

The primary goal of these research efforts is to shed light on the fluid-shift mechanism,its progress over time and its manifestations in the human body. In an initialapproach, the pressure in an arm vein was measured during the first Spacelab missionin 1983 and the German D-1 Spacelab mission in 1985. Attempts were made to obtaindata as early as possible in the mission. The astronauts were therefore trained to carryout venipuncture on themselves. On the D-1 mission, the first data were recorded asearly as 20 minutes after lift-off. Surprisingly, none of the values recorded exceededthose taken on the ground. Elevated values had been expected, due to the fluidengorgement within the upper part of the body. However, even in the peripheral veins,the pressures dropped by 7 – 8 cm H20. This means that pressures in the central partmust have fallen even more.

The data from the first Spacelab mission and the D-1 mission are shown in Figure2.1.6, where the values clearly tend to decrease even more with the length of themission.

These data were some of the first to show that the best terrestrial simulationexperiments cannot replace experiments actually carried out in the microgravityconditions of space. The result obtained was exactly the opposite of what wasexpected. An American group, using a non-invasive technique, also showed loweredCentral Venous Pressure (CVP) values, which declined progressively over the first threedays of flight. This cast some doubts on the methodologies used. These discrepanciesbetween ideas and hypotheses derivedfrom terrestrial experiments and theearly space findings promptedexperiments in which astronauts weresent into orbit with a venous catheter inplace. This was unthinkable in the mid-


tissues of the lower limbs, squeezing out the fluids contained in them. This alwaysoccurs when a person enters a swimming pool, for instance, or lies in a bath. Not onlydid gravitational physiologists provide a scientific explanation for the benefits of manyspa therapies, they also used this model to predict the adaptation of thecardiovascular system in space. This is a good example of how space physiology andmedicine has enriched our knowledge of the cardiovascular system’s workings on Earth.

The head-down-tilt (HDT) model of 6º is also often used to induce a cephalic fluid shift,thereby simulating microgravity effects, particularly on the cardiovascular system.Several groups in Germany, France and Denmark have used this model to prepare forexperiments in space. It could be shown, for example, that during immersion thevenous pressure in the central circulation zones increased by more than 10 mm Hg.This was also expected to happen in space.

These experiments were simulated by the observations made during NASA’s Skylabmissions. Very early in the mission, the astronauts observed that their legs began toshrink and that there was facial swelling. The superficial veins in the head and neckarea dilated, indicating they were full of blood. Measurements indicated that about2000 ml of fluid had left the lower limbs and must have been accommodated mostlyin the intra-thoracic circulation areas, in the same way as shown in Figure 2.1.1.5. ESAhas therefore given priority to experiments investigating these phenomena.

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Figure 2.1.1.5. The blood-volume distribution along man’s body axis when (A) standingfreely, and (B,C) immersed in water. Note the fluid shift and the central engorgement of fluidwhilst standing in water

Figure 2.1.1.6. Top to bottom, body weight,heart rate, venous pressure, andHematocrit values from eight crewmembers on the first Spacelab and theGerman D-1 Spacelab missions. Pre-flight,the crew gained weight, and their heartrate and venous pressure increased. In-flight venous pressures were rather low,with a tendency to fall even further. Post-flight, they were initially rather high, butlater decreased, to remain lower than pre-flight values for about a week. Note thatthe body weights were also lowered at thesame time

performance during flight, including cardiac output. At the beginning of the mission,the impedance of the thoracic section of the body decreased, implying that its fluidcontent was higher compared to the controls on the ground. In contrast, total bodyimpedance decreased, signalling an overall body-fluid loss. Later the fluid content ofthe thorax also decreased. The astronauts apparently dried out during the mission.Evidently, in space life is possible with a lower fluid content. Heart rate and bloodpressure varied very little. Here again, the question arises as to what will happen afterreturning from space? Does a good adaptation to space promote a safe return to Earth?

Prompted by earlier American reports that their astronauts already got ‘bird’s legs’and puffy faces in the early stages after lift-off, attempts were made during the D-2mission in 1992 and a 1993 Mir mission to quantify this fluid shift, particularly thatout of the superficial tissues. A simple ultrasound technique was used to measuretissue thickness at locations where a good back-wall echo from an underlying bonecould be expected, e.g. from the tibia and forehead. Tissue thickness in the tibiadecreased in space by 15%, whereas in the forehead it increased by 7%. From this, afluid shift of 200 ml from the superficial tissues of the lower limbs could be calculated,only 50 ml of which accumulated in tissues in the head that on Earth are kept dry bythe force of gravity. They are therefore totally unaccustomed to storing fluids. Althoughfluid is lost from these tissues during the mission, some still remains. Consequently,space travellers still perceive this fluid accumulation as a fullness of the head. Thesesymptoms can be replicated on Earth by, for instance, a 6° head-down-tilt (HDT)position. Prolonged fluid accumulations of this nature can also be observed in dialysispatients, who are unable to excrete fluids via the kidneys. Between dialysis sessions,they store about 50% of their water in these superficial tissues. This example showshow these space methods can also be applied in clinical medicine on Earth.

As early as 1981, a French group applied echocardiography in space aboard the Mirstation. During this short-duration flight, the left ventricular endiastolic volume waselevated on days 2 and 3 of the mission, indicating that the heart was well filled. Later,cardiac dimensions decreased below the pre-flight values. Cardiac output remainedelevated during this mission. These studies were continued later and the blood flow todifferent organs was analysed in detail. It was found that the total vascular resistancedecreased during spaceflight by 18%. The local vascular resistance was reduced inseveral areas, such as the brain, kidneys and the lower limbs.

In subsequent studies countermeasures were applied to prevent the fluid shift.Astronauts wore cuffs around their thighs that were inflated to prevent blood andtissue fluids returning from the lower limbs. Blood flow towards the lower limbs wasindeed reduced, because the vascular resistance was increased by 12%.

This is a passive fluid-shift countermeasure compared with exercise, which is an activecountermeasure. The effects seen in space depend not only upon the microgravity


seventies when venous-pressure measurements were first planned. Eight years later,an American and a Danish group were indeed able to show, using catheter tipspositioned close to the right atria, that central venous pressure fell by 5 to 8 mm Hgwhen entering microgravity.

As an example, the orginal recordings from one of the Danish experiments during theGerman D-2 Spacelab mission are presented in Figure 2.1.1.7. The upper trace givesthe pressure recordings, below which are the corresponding g-levels. During the8 minutes after lift-off, as the g-level increased, a slow but constant increase in CVP canbe seen between the time markers A and D, finally reaching nearly 18 mm Hg. Onentering microgravity, it then fell abruptly, below the control level seen on the left sideof the pressure trace. At D, for example, the astronaut was experiencing almost 3g.Nonetheless, it could be shown that during the first days in space intra-cardiac fillingand cardiac output were rather elevated, exactly as expected. These latter findingsstem in part from French and German groups using different methodologies, but thediscrepancy between low CVPs and high intra-thoracic filling volumes is still anunresolved problem requiring further investigation.

A group from the German Space Agency (DLR) quantified the fluid shift from the lowerlimbs towards the intra-thoracic parts of the circulation using an impedance techniquein which an alternating current is passed through the body and more than 80% of itis reconducted through superficial body layers. The water content of the tissuesdetermines the impedance. With this non-invasive technique, it was possible to makealmost continuous measurements and to gain considerable insight into cardiac

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Figure 2.1.1.7. Central Venous Pressure (CVP) measurements on one subject prior to launch(A – D) and after entering weightless conditions. The gravity levels are indicated on thelower trace (from Foldager et al.1996, J. Appl. Physiol. 81, 408)

started, the subjects had to undergo numerous tests, indicated on the right side of thefigure. Tilt-table tests were performed to ascertain orthostatic stability before and afterthe HDT session. The subjects also had to undergo Lower-Body Negative Pressure(LBNP) tests, in which the lower half of the body is fitted into an airtight box. With thehelp of a vacuum pump, a negative pressure around the tissues is created, whichinduces a shift in blood volume from the upper parts of the body towards the lowerlimbs. This simulates an orthostasis test, although the subject is actually in a supineposition. Even more importantly, the procedure can be used in space to induce a fluiddistribution as if on Earth. This test helps prepare the astronauts for re-entry into theEarth’s gravity, by familiarising them with the physiological changes occurring in theirbodies.

The lower part of Figure 2.1.1.8 is a schematic of the equipment used, many pieces ofwhich are mounted along the body axis. In this study, saline infusions were given tostudy fluid excretion under HDT conditions. These infusion experiments were laterrepeated in space.

Mention should also be made here of parabolic flight studies, in which periods ofabout 20 seconds of microgravity can be produced aboard an aircraft. A Danish groupused this method extensively in the late nineties to investigate the cardiovascular


environment, but also upon the circumstances under which the astronaut is living inthe space cabin, as was nicely demonstrated by the French experiments.

The blood volume in space is not only shifted upwards along the body axis, but it isalso reduced. Shortly after entering microgravity conditions, the plasma volumedecreases and later the red-cell volume also shrinks, making a close look at blood-volume control mechanisms essential. In space, erythropoietin values (EPO) arelowered; erythropoietin is a hormone excreted by the kidneys, which normallystimulates the production of red cells. EPO is excreted when the oxygen concentrationin the tissues is lowered, but as normal atmospheric gas pressures prevail in the spacecabin this is rather an unlikely cause. What then is the reason for the altered EPO levelsin space? An answer could lie in the EPO patterns after space flight, which aredrastically increased and this increase was always linked with lowered CVP values.This could also be demonstrated in other terrestrial experiments. For example, inspace-simulation studies like immersion, CVP was low following the period ofimmersion and EPO values began to rise. As Figure 2.1.1.6 shows, CVP values arelowered after landing but how the central circulation is linked to EPO secretion is stillan open question. Space physiologists believe there is a link between the filling volumeof the cardiovascular system and EPO secretion. Such a link has clinical implicationsthat need to be further explored in the future.

- Terrestrial Support Studies

Studies in space must be carefully prepared using ground-based simulation studies, asis illustrated by two fundamental aspects of space research that are often overlooked.The first is that research carried out on the same subject by a number of differentteams must be integrated operationally before any data are collected, not least for thewelfare of the subjects. Less obvious is the fact that integrated research requires thatan integrated model drives the scientific planning, protocols and methods.Experiments in space are carried out on a small number of subjects. In thesecircumstances, the strength of normal statistical methods is partially replaced by anew form of validity related to the scope of measurements across traditional researchboundaries in the same subject.

To satisfy these requirements, ESA and NASA, in collaboration with several nationalagencies in Europe, have carried out joint studies. One of these took place in Colognein 1988, in which subjects remained in a 6º HDT position for 10 days and manyparameters were studied before, during and after the session. 12 research groupsparticipated in this study, investigating predominantly the cardiovascular systemunder these conditions.

The significance of the integrated model can be seen in Figure 2.1.1.8. The upperportion shows the temporal history of the study. 12 days before the HDT session

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Figure 2.1.1.8. The timehistory of a Head-Down-Tilt (HDT) study. Thedifferent tests are listedon the right. The dottedbars indicate the times ofmeasurements

gravity in living systems in general, and in the human cardiovascular system inparticular. Attention has been directed to comparative physiology where, on the basisof many examples, it could be shown that gravity has deeply shaped both the formand function of the cardiovascular system. In the course of earlier experiments, it waslearned that concepts derived from Earth-based studies very often do not match therealities in space, which can be rather frustrating. It also opens up immenseperspectives, however, by demanding reconsideration of the concepts developed onEarth, thereby guaranteeing progress in our knowledge. For example, the design andapplication of new technologies in such fields as geriatrics or psycho-physiology arethe tangible outcome of our research efforts in space.

Europeans have already learned to co-operate closely with their neighbours in spacephysiology and medicine in order to be competitive in the race to live and work inspace, both now and in the more distant future.

Further Reading

Acta Physiologica Scandinavica 1992, 144 (Suppl. 604).

Bonting S.L. (Ed.) 1993, Advances in Space Biology and Medicine, Vol. 3, JAI Press Inc.,Greenwich, Connecticut.

Bonting S.L. (Ed.) 1996, Advances in Space Biology and Medicine, Vol. 5, JAI Press Inc.,Greenwich, Connecticut.

Hinghofer-Szalkay H.C. 1996, Physiology of cardiovascular, respiratory, interstitial,endocrine, immune, and muscular systems. In: Biological and Medical Research inSpace: An overview of life sciences research in microgravity, Springer, Berlin andHeidelberg, Chapter 2, pp. 107 – 153.

Howard P. 1981, Acceleration. In: Principles and Practice of Human Physiology,Academic Press, London – New York, Chapter 4, pp. 191 – 240.

The Clinical Investigator 1993, Vol. 71, No. 9.

Proceedings of the Skylab Life Sciences Symposium, 27 – 29 August 1974, Volumes Iand II, NASA TM X-58154, JSC, Houston.

Acknowledgements

The authors gratefully acknowledge the help and co-operation of the participatingastronauts during the various flights. Thanks are also due to the management of theEuropean, American, and Russian space agencies.


system under microgravity conditions. Many of the short-term effects seen in spacecould indeed be reproduced during the parabolic flights.

In the course of such studies, European physiological researchers have learned tocooperate in large groups, like particle physicists, to do ‘big science’. In this respect,space medicine must be regarded as a trend setter for life-sciences in general.

- Isolation Studies

In space, a person is not only disconnected physically from the Earth, but also isolatedfrom his/her normal social environment. An astronaut is confined together withcolleagues in a rather small cabin, from which escape is impossible. Isolation,confinement, overcrowding and stress can have a major impact on the human bodyin general, and on the cardiovascular system in particular. To study these effects, ESAconducted three isolation studies in which several different European groupsparticipated. Special emphasis was placed on psycho-physiology, which includedcardiovascular-system investigations.

The first study, in 1990, took place in Bergen (N), with six male subjects living for fourweeks in a small diving chamber. In 1992, another study was performed in Cologne inwhich only four subjects (1 female and 3 males) took part. Their confinement lastedsix weeks. In 1994/95, a similar study was performed in Moscow with three Russiansubjects, which lasted four months.

In the first study, where the subjects had a heavy workload, they felt stressed and theirblood pressures and heart rates went up significantly. For the second study in Cologne,the workload was deliberately reduced and none of the subjects displayed increasedblood pressure.

Another interesting point is body-weight management. Of the ten subjectsinvestigated in the first two studies, eight ended up with lower body weights, foursignificantly so. In the Moscow study, the three subjects, all of whom were obliged tostop smoking before going into isolation, gained considerable weight (5 to 12%). Thisis an example of how previous life style can play a role in the effects observed in space,which is another interesting lesson. Which factors, in the final analysis, lead to loss ofbody weight in space is still unclear, with all findings in space being overshadowed bythe effects of stress, confinement and isolation. Only terrestrial studies of the sortreported above will allow the true effects of the various parameters at work inmicrogravity on the human body to be distinguished.

2.1.1.3 Conclusions

Space physiology and medicine have led to the reconsideration of the role played by

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The basis for this concept is that the weight of the lung tissue pulling downwardskeeps the air spaces at the top of the lung expanded, so that they cannot expandmuch further during inspiration. In contrast, air spaces at the bottom of the lungs areless expanded and have a greater ability to expand during inspiration. Thus, there isan inherent ventilation gradient per unit lung volume, with much higher ventilation atthe bottom than at the top. Along with the greater mobility of the air spaces at thebottom, however, also comes an increased tendency for airway closure at low lungvolumes.

- Distribution of Perfusion

Early experiments with isolated animal lungs showed that the perfusion (blood flow)differences between the upper and lower parts of the lung could be accounted for bythe relationships with blood pressure in the vessels at different heights. Since thevertical pressure gradients in the pulmonary vascular system were gravity-inducedhydrostatic gradients, gravity was considered to be the principal determinant ofperfusion distribution in the lung (Fig. 2.1.2.1). In these experiments, perfusion perunit lung volume was assessed with a radio-isotope technique having a limitedresolution. It is not surprising, therefore, that more recent studies have revealedadditional, non-gravity-dependent perfusion differences between lung areas, whenmeasuring with higher resolution and in more than one dimension. However, eventhese more recent techniques have inherent limitations. The existence of non-gravity-dependent differences in local lung perfusion therefore remains a matter of somecontroversy.


2.1.2 Pulmonary Function in Space

D. Linnarsson


The lungs, the heart and the blood vessels are all links in a serially arranged transportsystem for the exchange of gases between the environment and the cells in the humanbody. Transport between the environment and the lungs is convective (‘normal flow’),driven by the cyclic expansion of the lung volume. Within the air spaces of the lungs,diffusive transport (i.e. movement of gas molecules driven by concentrationdifferences) dominates. It is also by diffusive transport that gases penetrate the thinmembrane that separates the most peripheral air spaces of the lungs from theirperfusing blood. Within the blood, gases are chemically bound to proteins in the redblood cells. The gas transfer between the lung gas and the blood is, to a large extent,determined by the rate of blood flow through the lungs. Thus, the functioning of thelungs cannot be seen in isolation. It must be analysed together with the cardiovascularfunctions, which determine the flow and volume of blood in the lungs.

Changes in the direction and/or the magnitude of the gravity vector have a profoundinfluence on lung function and blood circulation, since both the lungs and thecardiovascular system lack rigid structural elements. They are therefore easilydeformed by an external force such as gravity.

2.1.2.2 Background

The human lungs have a volume of 4 – 7 litres and a mass of 1 kg, about half of whichis blood. Tissues, including blood, and air spaces are arranged in a three-dimensionalelastic network and there is a 1000-fold difference between the densities of the tissuesand the gas. This combination of the easily deformed structure and the large densitydifference between its structural elements renders the lung especially susceptible tochanges in the magnitude and direction of gravity.

- Distribution of Ventilation

The present classical textbook concept of the influence of gravity on the distributionof ventilation in the lungs, illustrated in Figure 2.1.2.1, was developed partly fromstudies performed in a high-gravity environment.

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Figure 2.1.2.1. A schematic representation of the textbook concept of ventilation andperfusion distribution in the lung in normal gravity. In that concept, gravity tends to favourthe bottom parts of the lung with respect to local ventilation (breathing volume/unit timeand unit lung volume) and perfusion (blood flow/lung volume). The top to bottom gradientof local perfusion is larger than that for ventilation. Therefore, the ventilation/perfusionratio is highest at the top and lowest at the bottom. The vertical gradient of this ratio ismuch less than that of ventilation and of perfusion

Are these factors the structural properties, such as the dimensions and elastic forcesof the airways and blood vessels?

Question 4: ‘Are there feedback control mechanisms that synchronize ventilation andperfusion, but that cannot be discerned as long as gravity exerts a much largerinfluence?’

One such mechanism that has been proposed is a sensing of airway oxygenconcentration and an associated control of blood-vessel diameter. This would result inreduced blood flow to a lung area with low oxygen gas content caused, for example,by an obstructed local airway (hypoxic vasoconstriction). Another mechanismproposed is the generation, or the inhalation, of nitric oxide, a potent agent thatdilates the blood vessels, and which would act in well-ventilated lung areas. There aretheoretical foundations for such mechanisms, but the practical importance in healthand disease remains to be demonstrated.

Question 5: ‘What is the reason for the dramatic improvement seen when patientswith severe lung failure (acute respiratory distress syndrome, or ARDS) are treated ina prone (face-down) instead of a supine (face-up) position?’

The present understanding of the effects of gravity on lung function is not sufficient toexplain this potent treatment modality.

Question 6: ‘What are the characteristics of fluid exchange between lung tissue andblood?’

Excessive fluid accumulation in lung tissue and in the air spaces (lung oedema) is avery severe complication in heart failure. The unique changes in body-fluid volumeand its distribution seen in humans during spaceflight offer an equally uniqueopportunity to learn more about the mechanisms of fluid exchange in the lungs.

2.1.2.4 The Results of Space-Related Research and Future Potential

Ever since the first astronaut Yuri Gagarin returned safely from 70 minutes ofweightlessness in April 1961, it has gradually become obvious that the direpredictions of severe lung congestion were incorrect. During the early era of mannedspaceflight, only limited studies of lung function in space were performed. Later, thecombination of the US Space Shuttle and the European-built Spacelab provided asuitable laboratory environment for in-flight studies of human physiology. Researchgroups, both in the USA and in Europe, identified lung physiology as an area wheremuch could be learned about the normal effects of gravity on lung function fromexperiments carried out in space. Therefore, both NASA and ESA developed facilitiesfor pulmonary-function studies in sustained microgravity.


- Ventilation/Perfusion Ratio

A comparison of the distributions of ventilation and perfusion in Figure 2.1.2.1 revealsthat, in both processes, the bottom part is favoured, so that most of the gas exchangein the lungs takes place in the lower, most gravity affected part. The distributions ofthe two processes, however, are not congruent. The top-to-bottom gradient forventilation is less steep than that for perfusion. Consequently, the ventilation/perfusion ratio is highest at the top and lowest at the bottom. In other words, the toppart is relatively over-ventilated, despite a modest absolute ventilation per unit lungvolume, and the bottom part is relatively under-ventilated (with respect to perfusion)despite a large absolute ventilation per unit lung volume (Fig. 2.1.2.1, right).

2.1.2.3 Scientific and Clinical Problem Areas: Some Questions

Many of the basic concepts of treatment and diagnosis in pulmonary medicine andcritical care rest on the above concepts of how gravity influences lung function.However, for gas exchange in the lungs to result in satisfactory oxygenation of theblood leaving the lungs, it is the ventilation/perfusion ratio, rather than ventilation orperfusion, which must be homogeneously distributed throughout the lungs. Thus, thebasic scientific and clinical problems are to identify factors that influence the matchingof ventilation to perfusion, or vice versa.

Question 1: ‘Is it gravity that synchronises the distributions of ventilation and perfusion?’

As shown schematically in Figure 2.1.2.1, the ventilation/perfusion ratio is notperfectly homogeneous with respect to gravity, but is much closer to being so thaneither of the two separately involved processes. Another way to formulate thequestion is, will ventilation and blood perfusion in the lungs become uncoupled in theabsence of gravity? Will there be a failure in the gas transport from the lung gas to theblood? Here it should be remembered that early during the era of manned spaceflight,there were serious predictions of lung failure and inner drowning resulting from fluidcongestion in the lungs.

Question 2: ‘Is it instead gravity that is an impediment to ventilation and perfusion in thelungs, which is partly offset by similarities in the effect of gravity on the two processes?’

In other words, would the distributions of ventilation and perfusion becomehomogeneous in microgravity, with a resulting ideally homogeneous distribution ofventilation/perfusion ratios and a ‘perfect’ gas exchange?

Question 3: ‘If ventilation and perfusion do not become homogeneously distributed inthe lungs in microgravity, what are the factors that determine gas and blooddistributions in the lungs apart from gravity?’

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Short-term microgravity has been shown to result in well-defined changes inrespiratory mechanics. Functional residual capacity decreased by about 0.3 litrescompared to the upright control, to a value halfway between upright and supine. Thiswas most likely the result of an upward shift in the position of the diaphragm, whenthe weight of the abdominal organs was removed in microgravity. In sustainedmicrogravity, tidal volumes have been shown to be slightly reduced, but pulmonaryventilation of resting man was maintained owing to a slight increase in breathing rate.From a theoretical standpoint, vital capacity (VC) can be predicted to change in eitherdirection in microgravity; a more uniform lung expansion would favour an increase inVC, whereas an increased thoracic blood volume would favour a decrease. Also,expired and inspired VC determinations may differ, since an inspired VC would startwith a maximum expiratory effort, which would reduce the intra-thoracic bloodvolume. Expired VC, however, starts with a negative intra-thoracic pressure. It wouldtherefore be influenced by an increased tendency for intra-thoracic blood pooling.

An increase in expired VC values has been found after two weeks in space, suggestingthat, at that time, a more even alveolar expansion dominates over any tendency forincreased intra-thoracic blood pooling. In contrast, during the first days of spaceflight,expired VC was not increased compared to pre-flight upright control. This supports thenotion that an initially increased intra-thoracic blood volume counteracted the vital-capacity-increasing effect of a more even alveolar expansion.

- Ventilation Distribution

Classical methods for ground-based studies of ventilation distribution have beenimplemented during spaceflight. Astronauts inhaled one breath of an insoluble, non-toxic gas (with normal oxygen content), to study how it mixed with the gas remainingin the lung at the end of the preceding breath. It was found that different lung regionsdid not empty synchronously during expiration, and that these different lung regionshad received varying amounts of the inhaled tracer gas. Such asynchronous emptyingof regions and inhomogeneity of breath distribution were previously thought to becaused by gravity and, indeed, it is a regular finding in experiments in normal gravity.Subsequently, it was shown that in sustained microgravity, the wash-in time course ofan insoluble gas into the lungs was far from homogeneous.

- Distribution of Perfusion, Diffusion Capacity

To assess the anatomical distribution of perfusion within the lungs, radiographic orisotope-imaging techniques are required. So far, such methods are not available for useduring a space flight. Thus, more indirect techniques must be utilised. Figure 2.1.2.3shows a recording obtained during a recent parabolic flight, using the Advanced GasRespiratory Monitoring System, a facility developed by ESA for use on theInternational Space Station.


The first estimates of the distributions of ventilation and perfusion in the lungs inmicrogravity, derived from aircraft parabolic flights in 1978, suggested that bothventilation distribution and perfusion distribution became more homogeneous in theabsence of gravity. But there were signs of some residual inhomogeneity, which mayor may not have been ‘spill-over effects’ from the period of hypergravity that precedesthe short period of microgravity during parabolic flights.

Using similar methods, but now with the advantage of a sustained microgravityenvironment, the same research group, from the University of California, San Diego,studied lung function in astronauts during the Shuttle Spacelab flights SLS-1 in 1991and SLS-2 in 1993. Using more recent technology developed by ESA, a group ofEuropean and American investigators performed lung physiology experiments duringthe German Spacelab D-2 mission in 1993 (see Fig. 2.1.2.2). Two years later, they wereable to perform experiments in long-term microgravity conditions on a 179-day Mirflight. In parallel, parabolic-flight experimentation was conducted that wasinstrumental in the preparation and follow-up of the space experiments.

- Respiratory Mechanics

Russian researchers have shown that long-term spaceflight is associated with areduced peak expiratory flow and reduced forced vital capacity in 1 second.Significant reductions were observed after about 120 days of spaceflight. Thesechanges were attributed to deconditioning of the respiratory muscles. Thisexplanation seems plausible, because the postural muscles in the abdomen, thorax,shoulder, and neck are unloaded in microgravity. These muscles also serve asaccessory breathing muscles during a maximum effort. Alternative or co-existingexplanations that remain to be investigated are obstructive changes owing to aerosolinhalation, and changes in compliance and airway dimensions owing to local orgeneral interstitial oedema.

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Figure 2.1.2.2. AstronautHans Schlegel performinglung-function experimentsduring the GermanSpacelab D-1 mission


Essentially, inhalation of blood-soluble gases is utilised to assess the blood flow in thelungs. A breathing manoeuvre is first performed, to make the composition of solublegas in the lungs as even as possible. Then the breath is held to permit uptake of solublegas into the blood, and finally a slow expiration (expirogram) is made, where signs ofuneven gas uptake (and perfusion) can be detected. Such signs are heart-synchronousvariations of soluble gas concentration (cardiogenic oscillations) and end-expiratory(Phase-IV) gas-concentration deviations.

A similar indirect approach has been applied to humans during sustainedmicrogravity. Alveolar PCO2 and inter-regional PCO2 differences in the lung werereduced by vigorous hyperventilation. Carbon-dioxide expirograms were thenrecorded, following a breath hold. Observed Phase-III cardiogenic oscillations of PCO2were considered to be the result of PCO2 differences between lung units with differentperfusion-dependent rates of CO2 accumulation. Sustained microgravity wasassociated with a reduction – but not an elimination – of cardiogenic CO2 oscillationsin expired air. Phase-IV end-tidal deviations of PCO2, however, practically disappearedin microgravity. It was concluded that inhomogeneity still existed within regions thatwere not gravity-dependent. Gross inter-regional perfusion differences, however,probably disappeared in the absence of gravity.

Further studies of the rate of pulmonary blood flow and of the pulmonary diffusioncapacity have shown pulmonary perfusion to be increased during the initial days ofmicrogravity and to return towards pre-flight upright values after about one week.Membrane diffusing capacity became markedly improved in microgravity, comparedto both upright and supine pre-flight controls. This improvement was maintainedthroughout a 9 day microgravity period. The improved pulmonary diffusing capacitywas attributed to a more even distribution of capillary blood in the lungs and a moreefficient interface between the gas and the blood in the lungs.

The finding of an improved diffusing capacity speaks strongly against any generalisedinterstitial oedema in the lungs, something that was considered a risk, especially inthe period before large-scale manned space operations. For long-durationmicrogravity, however, there is no experimental support for excluding the possibilityof subclinical oedema in pulmonary tissues

Soluble gas uptake in the lungs can be used to assess the lung tissue volume. Suchmeasurements are relevant to the question of whether there is fluid transfer into thelung tissue (lung-tissue oedema). As described in Section 2.1.3, there is a markedtransfer of tissue fluid from the legs to the upper body during sustained microgravity.Contrary to expectations, the lung-tissue volume was reduced in flight, very much inproportion to the overall reduction in plasma volume.

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Figure 2.1.2.3. Assessment ofperfusion inhomogeneity in thelungs of a sitting subject, during aparabolic flight, using uptake of asoluble gas as measured by theAdvanced Gas RespiratoryMonitoring System. From the top:oxygen (% x 10), SF6 (% x 10), therespired gas flow, and an ECGmeasurement. (a) Time course of typicalprocedure, recorded in 1g. 34 – 40 sec, rapid re-breathing of25% O2, 1.6% SF6 (insoluble inblood). 40 – 52 sec, breathholding. 52 – 64 sec slowexhalation to residual volume,with fairly constant SF6 levelsuggesting adequate intra-pulmonary gas mixing. (b) Same as above, on expandedtime axis during expiration. Notethe marked cardiogenicoscillation of expired O2. (c) The same expiration inmicrogravity. Note the absence ofcardiogenic oscillations. (d) Following breath holdingduring initial high-g, thesubsequent expiration recordingmade in low-g shows thereappearance of cardiogenicoscillations.

Together, these data show thatcardiogenic oscillations of expiredO2 in 1g are due to unevenperfusion and O2 uptake in lungunits. It can be concluded thatthe absence of cardiogenic O2oscillations when both breathholding and expiration take placein microgravity must be causedby a more homogeneous O2content and perfusion betweenlung units, and not by an alteredmechanical interference betweenthe heart and lungs

(a)

(b)

(c)

(d)

of active feedback control mechanisms to synchronise ventilation and perfusion hasso far not been addressed during space-related research. However, the development ofhardware for in-flight analysis of nitric oxide has recently been proposed.

Question number five was: ‘What is the reason for the dramatic improvement that isseen when patients with severe lung failure are treated in a head-down instead of aface-up position?’ As yet, the issue of prone/supine differences in gas exchangeefficiency has only been addressed in normal and hypergravity. However, in futurespaceflight experiments, both supine and prone controls will be performed on theground for comparison with data obtained in space. Thus space experiments will beinstrumental in defining gravitational effects on the lungs over the whole range ofgravity directions and magnitudes.

The final question that was raised is: ‘What are the characteristics of fluid exchangebetween the lung tissue and the blood?’ The unexpected finding of a reducedpulmonary tissue volume in microgravity suggests that the understanding of the fluidexchange between the blood and the lung tissue is far from complete. This finding,however, deserves confirmation with improved instrumentation and more subjects.

Further Reading

Baranov V.M., Tikhonov M.A. & Kotov A.N. 1992, The external respiration and gasexchange in space missions, Acta Astronautica, 27, pp. 45 – 50.

Elliott,A.R., Prisk G.K., Guy H.J.B. & West J.B. 1994, Lung volumes during sustainedmicrogravity on Spacelab SLS-1, J. Appl. Physiol., 77(4), pp. 2005 – 2014.

Moore D., Bie P. & Oser H. (Eds.) 1996, Biological and Medical Research in Space,Springer, Berlin.

Prisk G.K., Elliott A.R., Guy H.J., Verbanck S., Paiva M. & West J.B. 1998, Multiple-breathwash-in of helium and sulfur hexafluoride in sustained microgravity, J. Appl. Physiol.,84(1), pp. 244 – 252.

Verbanck S., Linnarsson D., Prisk G.K. & Paiva M. 1996, Specific ventilation distributionin microgravity, J. Appl. Physiol., 80, pp. 458 – 1465.

Verbanck S., Larsson H., Linnarsson D., Prisk G.G., West J.B. & Paiva M. 1997,Pulmonary tissue volume, cardiac output, and diffusing capacity in sustainedmicrogravity, J. Appl. Physiol., 83(3), pp. 810 – 816.

Wantier M., Estenne M., Verbanck S., Prisk G.K. & Paiva M. 1998, Chest wall mechanicsin sustained microgravity, J. Appl. Physiol., 84(6), pp. 2060 – 2065.


- Scientific and Clinical Problem Areas

Some answers to the questions posed earlier have come from space-related research.

Concerning the first question that was posed: ‘Is it gravity that synchronises thedistributions of ventilation and perfusion?’, the answer is no. Gravity is not such anessential coordinating link between ventilation and perfusion that these processesbecome uncoupled in microgravity.

‘Is it, instead, that gravity is an impediment to ventilation and perfusion in the lungs,which is partly offset by similarities in the effect of gravity on the two processes?’ Theanswer is yes, to some extent the effects of gravity on ventilation and perfusiondistributions are not congruent, and so the two processes appear slightly better co-ordinated in microgravity than in normal gravity, as shown by an improved diffusioncapacity.

The third question was: ‘If ventilation and perfusion do not become homogeneouslydistributed in the lungs in microgravity, what are the factors that determine gas andblood distributions in the lungs apart from gravity?’ So far, space-related research hasnot revealed the nature of the factors that determine ventilation and perfusiondistributions in microgravity. Imaging techniques based on ionising radiation are todaythe only method available for determining the topographical distribution of ventilationand perfusion in the lung. An equivalent technology needs to be made available in space.

‘Are there feed-back control mechanisms that synchronise ventilation and perfusion,that cannot be discerned as long as gravity exerts a much larger influence?’ This issue

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Figure 2.1.2.4. Schematic of a modified concept for perfusion distribution in the lung,based upon recent space measurements. Contrary to predictions, indirect methodssuggest the presence of residual unevenness in lung perfusion in microgravity. Theanatomical distribution of this uneven perfusion has not yet been established and twopossible modes of non-gravity-dependent inhomogeneity are shown

when electrolyte concentrations are lowered. If, for example, one litre of pure water isabruptly consumed, the concentration of electrolytes is diminished by some 2% andthe surplus water is excreted within 2 – 3 hours.

When the intake of salt is increased, not only the salt but also water is retained in thebody, so that the concentration of electrolytes is maintained unchanged by themechanism described above. Therefore, an increase in salt intake leads to fluid volumeexpansion. This is sensed by receptors, which through nerve signals inform the centralnervous system of the increase in volume. Through another set of nerve signals,messages are sent to the kidneys to excrete more sodium. The urinary excretion rateof water will subsequently also increase to prevent the concentration of electrolytesfrom decreasing. Thus, the water-regulating mechanisms are activated primarily bychanges in the concentrations of electrolytes in blood and tissue fluids, and thesodium-regulating mechanisms by changes in fluid volume.

The sensors for detecting changes in electrolyte concentrations reside in the brain andare connected to the main water-regulating hormone, vasopressin (antidiuretichormone). The location of the receptors for detecting fluid volume is still debated, butthey are generally thought to be located in the heart chambers, adjacent vessels andcentral arteries. Through nerve connections, they communicate with sodium-regulating hormones and the kidneys. In addition, peptides in the heart, brain, andkidneys can be released by nerve activity or, in regard to the heart, directly bymechanical stretching so that excretion of salt can be facilitated.

At present, it is fair to say that the qualitative significance of each of the above-mentioned systems has largely been determined, whereas the quantitativesignificance has not. Because the systems are sensitive to changes in gravitationalstress, space research can contribute to quantifying the significance of each of thesesystems.

2.1.3.3 Gravity and Fluid Volume Regulation

That the water- and salt-regulating mechanisms in humans are sensitive to changes ingravitational stress has been known for decades. Humans who are upright excrete lesswater and salt in their urine than those who are supine. The reason is that in theupright position one retains as much salt and water as possible, in order to maintainan adequate blood pressure to the brain. On the other hand, when humans are supine,the body perceives the amount of blood and fluid in the heart as being exaggerated.Therefore, water- and salt-excreting mechanisms are activated.

The mechanisms of the posture-induced changes in urinary water and salt excretionare thought, as described above, to be primarily stimulated by fluid-volume receptorsin and/or close to the heart. When humans are supine, the heart and nearby vessels


2.1.3 Fluid and Electrolyte Regulation and Blood Components

P. Norsk


In order to sustain life, the amounts of water and salt (fluid and electrolytes) in thebody are rigorously controlled within narrow limits, despite large fluctuations inintake. It is, however, surprising that despite more than a hundred years of research,the basic mechanisms of this life-sustaining system are not fully understood. Onereason for this lack of understanding is that the water and salt regulation is complexand involves elements of several physiological systems such as the circulation,hormones, nerves, and kidneys. Another reason is that the methodology andexperimental procedures have been insufficient.

With the advent of manned spaceflight, two possibilities emerged with regard toresearch into fluid and electrolyte regulation: (i) weightlessness could be used as a tool,to stimulate the body in a way that was not possible before, and (ii) the methodologyfor measuring the physiological variables could be improved by the spaceprogrammes.

The reason that weightlessness is unique for understanding how the body regulatesthe amount of salt and water is that the fluid-volume control mechanisms aresensitive to changes in gravity. During the course of daily life on Earth, there arefluctuations in blood and fluid along the body axis as the subject’s posture changeswith respect to the gravity vector. In the microgravity environment of space, thoselarge fluctuations are abolished. Because those fluctuations affect the excretion ratesof water and salt in the urine, more information can be gained by performingexperiments in space. Microgravity thereby becomes an additional, advanced tool instudies to try to answer one of the fundamental questions of physiology: How doesthe body regulate the salt and water balance?

2.1.3.2 Basic Fluid and Electrolyte Regulation

The water- and salt-controlling mechanisms constitute a complex interaction betweenthe cardiovascular reflexes, fluid- and electrolyte-regulating hormones, and thekidneys. Furthermore, physical factors such as blood pressure and dilution of theblood with tissue fluid also play significant roles. Finally, the concentration ofelectrolytes in the blood and tissue fluids determines the excretion rate of water inurine. If the electrolyte concentration is high, this will be perceived as thirst, so thatdrinking is increased and urinary water excretion diminished. It is the reverse situation

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Thus, during the initial hours of a spaceflight, the heart and adjacent vessels aredistended. This should, according to the results of simulation models on the ground,initiate an increased excretion rate of water and salt in the urine, with a resultant lossin body fluid.

2.1.3.5 Expected Responses in Space

During the initial decades of manned spaceflight, expectations of how physiologicalsystems would respond to weightlessness were based on the results of simulationexperiments. In this context, the head-down bed-rest model has been preferred towater immersion, because it is more easily applicable for interventions of several daysor weeks, although its true applicability in this regard has never been directly tested.The model was considered adequate for simulating the effects of weightlessness onfluid and electrolyte control, because the astronauts usually lose 2 – 4 kg of bodymass during the initial days of flight. This mass loss was considered to consistprimarily of electrolytes and fluid. Furthermore, the volume of blood is reduced bysome 10 – 17%. Head-down bed rest also reduces blood volume, by approximately10%. Hence the head-down bed-rest model was thought to simulate the effects ofweightlessness reasonably well.

The mechanisms of the augmented urinary excretion rates of salt and water duringhead-down bed rest are depicted in Figure 2.1.3.1. Head-down bed rest induces anincrease in the blood volume in the heart and nearby vessels, which through themechanisms described earlier promotes the higher urinary excretion rates of salt andwater. A new state of adaptation is then achieved, with a diminished fluid and bloodvolume.


are distended, because blood moves from the legs towards the head. The opposite isthe case when humans are upright. During water immersion, the movement of bloodand fluid towards the upper body parts is more pronounced. This leads to augmentedincreases in water and salt excretion by the kidneys, which exceed those of a posturechange from upright to supine.

Even before manned spaceflight, it was anticipated that weightlessness would causeincreased excretion of water and salt in urine. This expectation was based upon theresults of water immersion experiments. Water immersion was, and is still by some,considered an analogue of weightlessness. It induces salt loss at a rate six times higherthan when the subjects are seated in air. At the same time, the loss of water is morethan doubled. Therefore, before humans went into space, it was expected that similarfluid and salt excreting mechanisms would be activated by weightlessness and thatthe astronauts would lose water and salt through the kidneys.

2.1.3.4 Distension of the Heart in Microgravity

The question of whether the heart is distended during the initial hours of spaceflightby weightlessness is important. As described previously, distension of the heart isthought to stimulate urine production. In the early studies from the Apollo and Skylabmissions in the 1960s and 70s, the astronauts reported ‘puffy’ faces and feelings offullness in the head. This was regarded as a consequence of blood and fluidtransferring from the lower to the upper parts of the body. Another indicationsupporting this idea was the decrease in the size of the legs. Therefore, from the earlydays of manned spaceflight, indirect evidence supported the hypothesis that blood ismoved to the heart, adjacent vessels and head during weightlessness.

More direct evidence that the blood supply to the heart is augmented at the beginningof spaceflight has been obtained in the 1980s and 90s. By imaging the heart chambersusing ultrasound techniques (echocardiography), it was observed that during theinitial hours of spaceflight the heart is distended. The heart is even larger than insupine humans on the ground. However, the mechanisms causing this distension arenot as originally anticipated. Direct pressure measurements show that the pressure inthe regions outside the heart is decreased. This decreased pressure on the outsidesurface of the heart augments the distension, and might be caused by a change in theconfiguration of the lungs and chest wall. Distension of the heart at the beginning of aspaceflight is therefore not only caused by passive movement of blood and fluid fromthe legs to the upper parts of the body, it is also caused by an anatomical change inthe configuration of the chest walls and lungs. This is a new discovery and one thathas been confirmed by experiments during parabolic flights with 20 seconds ofweightlessness.

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Figure 2.1.3.1. The old concept of howfluid and blood volume were reduced byweightlessness, based on the results ofsimulation experiments (e.g. head-downbed rest). When changing posture fromupright to 6° head-down, blood and fluidfrom the lower parts of the body aremoved towards the heart and head. Theheart is distended by an increased bloodsupply, which through nerve connectionsand hormones induces an increased lossof water and salt in urine. This leads to areduction in blood volume. When the salt-and water-excreting mechanisms in head-down bed-rest subjects are stimulated byinfusion of salt solutions or drinking-waterloads, urine output still remains high

Old concept

Weightless simulation

Heart distension

Fluid excreting hormone effect

Increased urine output

Reduced blood volume

The pattern of an attenuated urine output of water and salt in space followingstimulation by infusion and the high activity of the sympathetic nervous system fittogether, because the latter might explain the former. However, it does not fit with the expectations from the results of the head-down bed-rest model. Therefore, theunderstanding of how gravity and weightlessness modulate the fluid and electrolyteregulation in humans was insufficient before the results of spaceflight experimentswere available.

2.1.3.7 A New Concept

The current textbook descriptions are unable to explain why: – urine production is not increased during the initial hours of spaceflight– it is not stimulated to the same degree, by a water and salt load, in space as during

supine ground-based conditions– the fluid-retaining sympathetic nervous activity is high in space.

A new concept must therefore be developed.


When water and salt stimuli (e. g. infusion of salt solutions or drinking-water loads) areapplied to head-down bed-rested humans, the urinary excretion rates stay highdespite reductions in blood volume and body fluids. This observation indicates that itis the augmented urinary excretion rates of salt and water during the initial phase ofbed rest that accounts for the fluid and blood volume deficit.

2.1.3.6 Surprising Responses in Space

Spaceflight results during the past 20 years indicate that the generally acceptedscheme (Fig. 2.1.3.1) whereby astronauts lose water and salt in space is not correct.There are no indications that urine output is increased in space; in fact there areindications to the contrary. Already during the Apollo flights to the Moon, it wasobserved that the urine outputs were always lower than on the ground, even thoughthe astronauts lost several kilogrammes of body mass. The same was observed duringthe Skylab flights some years later. It was suggested that the low urine outputs duringthe initial phase of flight were caused by less fluid intake and that the urine outputswere in fact augmented compared to the intake. This notion has not, however, beensubstantiated by direct observations. Recent studies on the Shuttle and on the RussianMir station indicate that the water and salt output in the urine is not increased.

If the scheme described in Figure 2.1.3.1 were correct, one would expect urine outputfollowing a water and salt stimulus to be the same in space as during head-down bedrest, but this is not the case. During the German D-2 Spacelab mission, a salt solutionwith the same tonicity as body fluids was infused into the astronauts. The in-flightconditions were standardised so that, except for weightlessness, they resembled thoseof the ground-based control. Urine output was stimulated by the infusion, but to amuch lesser degree than when the astronauts were supine on the ground. This wasnot anticipated. The urine output in space was therefore attenuated, which was notexpected on the basis of the results from ground-based simulation studies. Resultsfrom the Euromir ’95 mission confirm that urine output following the drinking of wateris also attenuated and that it was not predictable from long-term simulation by head-down bed rest.

Another unexpected finding in space during the D-2 mission was that the nervousactivity, which controls the degree of constriction of the blood vessels and canmodulate urine production (sympathetic nervous activity), was higher thananticipated (Fig. 2.1.3.2). The increased sympathetic nervous activity was determinedby estimating the concentration in the blood of a hormone, norepinephrine, which isa component of this system. Usually, the activity of this portion of the nervous systemis low during head-down bed rest. There is no apparent reason why this system’sactivity should be high in space, because there is no obvious reason for the vessels toconstrict or for the kidneys to produce less urine. These observations were confirmedlater by American and European scientists during the Neurolab mission in 1998.

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Figure 2.1.3.2. Concentration of norepinephrine (NE) in the blood of four astronauts,averaged over a 4-hour period during: (1) supine conditions on the ground, (2) uprightseated conditions on the ground, and (3) after adapting to 4 – 5 days of weightlessness(flight) on the Shuttle Spacelab D-2 mission. The highest values were obtained during flight(* indicates a statistically significant change). This was unexpected because head-downbed rest produces low values. The high NE levels indicate that sympathetic nervousactivity is high with contraction of blood vessels and retention by the kidneys of salt andwater (from Norsk et al. 1995, J. Appl. Physiol., 78, p. 2253)

2.1.3.9 Prolonged Spaceflight – A Testbed for Heart Disease?

The new concept (Fig. 2.1.3.3) in which the gravity-induced mechanical pressure onthe body tissues in supine humans has a pronounced effect on fluid and electrolyteregulation and some of the associated blood components, is of relevance forunderstanding the mechanisms of disease. In patients with heart failure, fluid andelectrolytes are accumulated in the body, because the heart cannot supply the organswith blood as efficiently as in healthy people. The accumulation of fluid leads tooedema and to a further deterioration in condition, thus establishing a vicious circle.Furthermore, heart-failure patients might experience difficulties when supine due tothe gravity-induced pressure on the heart. Thus, the transverse gravitational stress insupine heart patients might explain some of the disease patterns. When a patient isupright, however, the weak heart has difficulty in maintaining blood pressure to thebrain. Gravity is therefore a problem for heart-failure patients (Fig. 2.1.3.4).


Firstly, the diminished blood volume in space cannot be due solely to augmented urineproduction. Recent investigations indicate that the astronauts drink and eat lessduring flight. The reason for the reduced food and fluid intake is not known. It mightbe due to some degree of space sickness or to some as yet undetermined disturbancesof the central nervous system by weightlessness. Secondly, blood volume might bereduced more by microgravity than by head-down bed rest, because there areindications that weightlessness promotes movement of fluid from blood to tissues.This might be caused by the total lack of gravity-induced tissue compression, whichthe body is continuously exposed to on the ground, particularly when supine. Thirdly,a minor contribution to the loss of blood stems from the fact that the heart isdistended during the initial hours of weightlessness. This distension, probably actingthrough nerves and hormones, to some degree augments urine production.

Therefore, spaceflight might initially produce a fluid and blood volume deficit causedprimarily by: (i) decreased intake of food and fluids, and (ii) movement of fluid fromblood to tissues (extravasation). In space, blood volume is thereby reduced more thanduring head-down bed rest. This blood volume deficit could lead to activation of fluidand electrolyte retaining systems, and to low urine production and low urineresponses to water and salt stimuli. This new hypothesis is depicted in Figure 2.1.3.3.

The fact that the urinary excretion rates of salt and water are attenuated in space,following stimulation by infusion or drinking water, indicates that the blood-volumedeficit is not primarily caused by urinary losses at the beginning of spaceflight. Itindicates rather that the urinary attenuations following infusion are secondary tothose of blood-volume contraction (Fig. 2.1.3.3). This is in contrast to the effects ofhead-down bed rest, where the augmented urinary responses to water and saltinfusions indicate that the initial urinary losses are the primary causes of the volumedeficit (Fig. 2.1.3.1).

2.1.3.8 A New Simulation Model

The discrepant effects on the kidneys of head-down bed rest and of weightlessnessindicate that bed rest is not a valid simulation model. Therefore, another more reliablemodel should be developed. The mechanisms of the discrepant effects ofweightlessness and bed rest are at present unknown. As noted above, one explanationmight be that during head-down bed rest the supine body is continuously compressedby its own weight. This might modulate the relationship between the heart-, fluid- andelectrolyte-regulating hormones, and the kidneys. That the heart is compressed insupine humans is indicated by recent results from parabolic flights, where it has beendemonstrated that the size of the heart promptly increases during weightlessness.

Whether water immersion for days, weeks or months simulates the effects ofweightlessness in space better remains to be determined.

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New concept

Weightlessness

Central Heart No gravitationalsystem distension? tissue compression

Reduced fluid Increased urine Fluid from bloodintake output? to tissue

Reduced blood volume

Fluid retaining hormone effect

Decreased urine response

Figure 2.1.3.3. A suggested new concept for how blood volume is reduced duringspaceflight. Immediately after launch, weightlessness induces: (i) a decreased fluid intake,(ii) absorption of fluid by the tissues from the blood, and (iii) distension of the heart. Theseeffects all lead to a reduced blood volume, which activates fluid-retaining hormonesystems and sympathetic nerves (Fig. 2.1.3.2), which in turn leads to secondary low urineresponses to water and salt loads. According to this hypothesis, the reduction in bloodvolume is not caused primarily by the kidneys, contrary to the old hypothesis (Fig. 2.1.3.1)based on simulation experiments

those of ground-based simulations. Consequently, the concept of how weightlesnessand gravity modulate the regulation of body fluids and the associated bloodcomponents must be revised, and a new simulation model developed. In addition, theinformation obtained from space might be of relevance for understanding how gravitycauses a deterioration in the fluid and electrolyte balance in heart-failure patients.

The surprising observations in space regarding the mechanisms of fluid-volumecontrol in humans indicate that our knowledge of the effects of gravity on this systemis insufficient. Furthermore, the conclusion that the well-known simulation model ofhead-down bed rest does not in fact simulate the effects of spaceflight indicates thatthe effect of compression of the recumbent human body by gravity is not wellunderstood. Until the advent of manned spaceflight, only the effects of gravity onupright versus supine humans were explored. The results from space have shown thatthis approach is too narrow and simplistic.

Exploiting spaceflight in the future to obtain more information about how gravityaffects the human body may lead to improvements in the treatment of severaldiseases. Gravity has a pronounced effect on fluid-volume control in heart patients.When the heart is weakened, it is more difficult for the cardiovascular system toovercome the negative effects of gravity. This leads to salt and water accumulation inthe diseased body, which in turn has a deleterious effect on the heart. At present, notenough knowledge has been gained about how gravity affects heart patients, and towhat degree it is responsible for the accumulation of water and salt. Research in spacemight well improve our knowledge on this issue.

In space, the water- and salt-regulating mechanisms adapt to a state that resemblesthat of being upright on the ground. Before the initiation of the manned spaceflightprogrammes, the expectation was that the physiological systems would adapt to alevel which more resembled that of being ground-based supine. Spaceflight data have,however, shown that the body recognises the upright position as the equilibrium andthe set point. This is logical because humans are mostly upright for about two thirdsof the day. Acute weightlessness is therefore an unstable condition where, during theinitial few days, the heart, hormones, blood volume and kidneys adapt to a state withthe same values as those observed in the upright ground-based condition.

In the future, this area of space research needs to focus on the mechanisms that giverise to the surprising observations regarding water and salt balance. This will requirephysiological equipment for monitoring of the heart, blood pressure, hormoneconcentrations, and kidneys. In addition, the mineral content of the food must beaccurately measured. The equipment should be more sensitive than it is today,because even small inaccuracies will, over long monitoring periods, produce largeerrors. Non-invasive, accurate physiological equipment is therefore an essentialrequirement for future space research.


Heart patients also sometimes exhibit high levels of sympathetic nervous activity andof fluid- and sodium-retaining hormones. Astronauts in space exhibit the samepatterns. The mechanisms of these augmented hormone releases and of sympatheticnervous activity are, however, different when comparing heart-failure patients withweightless astronauts, because the astronauts are still healthy. On the other hand, theactivated hormone secretions and nervous activity might be caused by a diminishedblood supply to the arteries. In the heart patients, this is because their heart is weak,while in the astronauts in space it is because their blood volume is reduced (Fig. 2.1.3.3). Therefore, prolonged spaceflight might constitute a testbed forinvestigating certain aspects of the mechanisms of heart disease.

By comparing the cardiovascular, hormonal and kidney variables of: (i) healthyastronauts on the ground, (ii) astronauts in space, and (iii) heart patients, the followingquestion might be answered: ‘How can astronauts, during prolonged spaceflight,exhibit the same physiological patterns as heart-failure patients without being ill?’ Ananswer to this question might reveal new disease mechanisms of importance fordeveloping new treatments.

2.1.3.10 Conclusions and Future Research

In summary, fluid and electrolyte regulation and the changes in associated bloodcomponents in humans are modulated by gravitational stress. Weightlessness istherefore a unique tool for obtaining more information about integrated fluid volumecontrol. Results from space, however, have been unexpected and not predictable from

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Figure 2.1.3.4. Heart-failure patients exhibit salt and water retention, with theaccumulation of fluid in the tissues (oedema). The results of space and parabolic-flightinvestigations indicate that the heart is compressed in supine humans by gravity, whichmay cause further deterioration in the condition of heart patients. Investigations in spacemay reveal to what degree gravity affects the failing heart and how to counteract it

2.1.4 Muscles in Space

P.E. di Prampero, M.V. Narici & P.A. Tesch


For man to remain in space for periods beyond a few months and for any futureprojects that plan to send astronauts to other planets, the negative effects ofmicrogravity on muscle and skeletal (see Section 2.1.5) systems must be overcome.Since the beginning of the spaceflight era, it was believed that extendedweightlessness alters bone and muscle integrity and function. In muscle, thesechanges comprise loss of mass, force and power and increased muscle fatigue andabnormal reflex patterns.

These changes are due to multiple factors, among which increased muscle proteindegradation and altered neuromuscular control are probably the most important. Theyare brought about by the absence of the constant pull of gravity. During long-termspace missions, muscle de-conditioning due to lack of weight-bearing activities couldlimit the crew’s ability to work in space, or to operate effectively on the surface of Marsor any other planets, or to egress the spacecraft in an emergency landing. Muscleatrophy and weakness are of particular concern when the transition from 0g to 1gtakes place. At that point, which occurs on returning to Earth from space, the musculo-skeletal system suddenly has to bear the force of gravity again. Hence, the integrity ofthe motor system is essential for the accomplishment of human movement.Maintenance of posture and displacement of body weight is achieved through theaction of muscles acting across joints, particularly the extensor muscles of the lowerlimbs. Loss of muscle (atrophy) eventually results in weakness and poor mobility. It isalso a common condition resulting from bed confinement, casting, injury and traumaand reduced physical activity. The ageing process also involves loss of muscle mass,which in addition to disuse atrophy is referred to as ‘sarcopenia’. Although both disusemuscle atrophy and sarcopenia are considered major causes of muscle weakness andmobility impairment, the underlying mechanisms, their development as a function oftime, and functional implications are not yet fully understood.

The weightless condition of spaceflight therefore provides a unique environment forstudying the effects of long-term muscle disuse on muscle function, physicalperformance and health. The experience gained from space research is valuable forunderstanding the effects of severe muscle disuse on Earth, its functionalrepercussions, and for its prevention by means of physical and pharmacologicalcountermeasures. Efforts to understand and mitigate the phenomenon of muscleatrophy and weakness are therefore imperative. Learning from these studies is


Further Reading

Bie P., Bestle M.H &.Johansen L.B. 1996, Kidney function and fluid homostasis. In:Biological and Medical Research in Space, Springer.

Miller J.A.., Tobe S.W. & Skorecki K.L. 1996, Control of extracellular fluid volume and thepathophysiology of edema formation. In: The Kidney (Ed. B.M. Brenner), W.B. SaundersComp. 5th Edition, Vol. 2, pp. 817 – 872.

Norsk P. & Epstein M. 1991, Manned space flight and the kidney (Review), Am. J.Nephrol., 11, pp. 81 – 97.

Norsk P. 1996, Role of arginine vasopressin in the regulation of extracellular fluidvolume, Med. Sci. Sports Exerc., 28 (10 Suppl.), pp. S36 – S41.

Norsk P., Christensen N.J., Bie P., Gabrielsen A., Heer M. & Drummer C. 2000,Unexpected renal responses in space, The Lancet, 356, pp. 1577 – 1578.

Robertson G. L. & Berl T. 1996, Pathophysiology of water metabolism. In: The Kidney(Ed. B.M. Brenner), W.B. Saunders Comp. 5th Edition, Vol. 1, pp. 873 – 928.

Watenpaugh D.E. & Hargens A.R. 1996, The cardiovascular system in microgravity. In: Handbook of Environmental Physiology (Eds. M.J. Fregly & C. M. Blatteis), Am.Physiol. Soc., Sect. 4, Vol. I, , Chap. 29, pp. 631 – 674.

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When the force applied to the muscle during stimulation is less than the maximumtension that the muscle can develop, upon contraction the muscle shortens (isotonicconcentric contraction). This produces external mechanical work, given by theproduct of the force and the distance shortened along the direction of application ofthe force. If, however, the force applied to the muscle is greater than its maximumtension, then upon contraction the muscle is stretched (isotonic eccentric contraction),thus absorbing external work.

Finally, if the muscle is attached to a rigid structure, the muscle’s output uponcontraction is tension only, without any shortening, and hence no external work isperformed (isometric contraction). Thus contraction and shortening are notsynonymous: upon contraction the length of the muscle can become shorter, longeror remain unchanged, depending upon the force applied. In all cases, however, asubstantial fraction of the chemical energy utilised by the muscle to perform work orto develop tension is dissipated as heat. During everyday exercise such as bicyclepedalling, the external mechanical work performed is in the order of 25% of the totalenergy consumed by the muscle, the remaining 75% being dissipated as heat.

The mechanical power (work per unit of time) developed by a given muscle dependsupon the duration of the effort. A young man of 70 kg body mass, for example, iscapable of sustaining 0.20 – 0.25 kW for about 10 to 15 min of whole-body exercise,such as cycling or rowing. Power may exceed 1.2 – 1.5 kW in very brief (0.3 sec)explosive exercises, such as the maximal vertical jump off both feet. In athletes ofsimilar body mass, powers may reach 0.5 and 2.0 kW for long-duration and explosiveexercise, respectively.

- Simulation of Weightless Conditions

Although microgravity cannot be simulated on Earth, its chronic effects on themusculo-skeletal system can be simulated. Indeed, various techniques are availablethat can be employed in man as space analogues to prevent weight-bearing bymuscles and thus simulating the unloading that occurs in space:

(i) Bed rest, in which healthy subjects are confined rigorously in bed. Typically such anintervention uses a 6 deg head-down tilt to allow for and simulate fluid shifts thatoccur in space.

(ii) Lower-limb suspension in humans, in which one leg is unloaded by means ofappropriate straps, and/or by elevating the sole of the contra-lateral shoe.Ambulatory activities are carried out using crutches.

(iii) ‘Dry water-immersion’, in which healthy subjects are immersed in water fromwhich they are separated by means of a layer of impermeable tissue. Their bodyweight is therefore supported almost completely by the buoyancy lift, but thesubject’s skin remains dry, thereby permitting rather long periods of immersion.


essential for generating technological advances and new concepts for counteractingmuscle wasting in space and on Earth.

- Muscle Form and Function

The ability to move is so characteristic of living forms that motility and contractilityhave long been considered essential properties of life itself. In primitive life forms, thecontractile function is served by specialised subcellular structures, called ‘cilia’ or‘flagella’. In higher animals, differentiated muscle fibres are organised into effectororgans, or ‘muscles’. Each muscle fibre transforms chemical energy into work in a co-ordinated manner, controlled by the nervous system.

In vertebrates, skeletal muscles are typically attached across articulated joints of rigidskeletons, with the muscle fibres being linked to tendons that, in turn, attach to thebones on both sides of the joint. Muscle fibres are organised into motor units, whereina single nerve cell, called a ‘motor neuron’, innervates several muscle fibres. Thecollection of fibres innervated by a single motor neuron is called a ‘motor unit’. Thenumber of fibres in a motor unit determines the finesse with which the contraction ofa particular muscle can be regulated; the smaller the number of fibres, the greater thefinesse. Skeletal muscle responds to an adequate stimulus, be it intrinsic (nervous) orextrinsic (electrical), giving a twitch, i.e. a brief contraction, followed by relaxation. Thetime course of the twitch depends on the composition of the muscle in terms ofmuscle fibres. Indeed, broadly speaking, muscle fibres belong to two types: ‘fasttwitch’ (or Type-2) fibres and ‘slow- twitch’ (or Type-1) fibres.

Fast-twitch fibres are characterised by a large diameter. They rely mainly on anaerobicmetabolism (they do not need oxygen), they are pale in colour (hence in the oldliterature they were referred to as ‘white’ fibres), they attain their peak tension in arelatively short time (about 10 – 20 ms), they are easily fatigued and their contractionis forceful. Slow-twitch fibres lie at the other end of the spectrum. They are of smalldiameter, rely on aerobic metabolism (they need oxygen), they are red, attain their peaktension (substantially less that that of the fast-twitch fibres) over a relatively long period(70 – 100 ms), and they are fatigue-resistant. For example, the breast of a chicken is atypically white muscle, whereas chicken legs contain red muscle. In contrast to thechicken, the muscles of most mammals, humans included, have a variable compositionof fast- and slow-twitch fibres, and are intermingled in a mosaic pattern. Muscle-fibre-type composition is set by both genetic and environmental factors.

If a second stimulus is given to the muscle before the mechanical response to the firsthas completely ceased, summation occurs. If the stimuli are repeated regularly at arapid enough frequency, the result is a fused contraction, termed ‘tetanus’, duringwhich the tension is maintained at a constant level that is three to five times higherthan that of a single twitch.

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in rats, protein synthesis decreased and protein degradation increased. In the followingtwo weeks, equilibrium between synthesis and degradation was again achieved, thusstabilising muscle protein content, albeit at a lower level than before hind-limbsuspension. Experiments performed during long-term (more than 3 months) spaceflightonboard the Mir space station have revealed a decrease of about 15% in the rate ofprotein synthesis in humans. Even if the effects of a decreased dietary intake could notbe ruled out, recent experiments performed on cultured avian muscle cells duringspaceflight have shown that microgravity directly depresses protein synthesis.

Whereas most studies on mice and rats have reported preferential atrophy of the slow-twitch fibres after both simulated (hind-limb suspension) and actual microgravityexposure, albeit with some differences between the two conditions, the data obtainedin humans does not show such a consistent trend. Indeed, following four to six weeksof either bed rest or lower-limb unloading, studies show a similar atrophy of slow- andfast-twitch fibres. Simulated and actual spaceflight may result in a greatersusceptibility to damage upon reloading of animal and human muscles. The damageis characterised by eccentric contraction-like lesions, showing disruption of musclestructure followed by rapid repair processes. Muscle damage is accompanied bymicro-circulatory changes and interstitial oedema, which are responsible for muscleswelling. At present, evidence of greater susceptibility to human muscle damage afterspaceflight is sparse, since few studies have addressed this particular question, so far.


Although these models are, at present, the best available methods for simulating theeffects of microgravity on Earth, it must be remembered that the body is still subjectedto the pull of gravity even if unloaded. Furthermore, the effect of microgravity on thevestibular system and its effect on motor control cannot be mimicked on Earth usingthe above three paradigms. Therefore, although considerable information may beobtained from research using these models, there is no real analogue to spaceflight.Thus, the effects of microgravity on the motor system can really only be studied inspace.

The following discussion briefly reviews the changes in muscle structure and functionthat occur in microgravity, focusing on human studies. The structural alterations thatfollow simulated or actual microgravity are reported in the first section. The secondsection is devoted to the functional changes, and the final one describes potentialexercise countermeasures. The concluding section addresses topics to be consideredfor future research.

2.1.4.2 Structural Alterations

The results of human and animal studies performed in simulated or actualmicrogravity consistently show that muscle undergoes substantial atrophy. This isdue to a decrease in muscle fibre size, with no apparent change in fibre number.Studies also show that atrophy is considerably greater for postural muscles, i.e. forthose muscles that, on Earth, support the weight of the body, as compared to the non-postural muscles, which undergo only marginal changes. In addition, substantialdifferences exist also amongst the postural muscles themselves. The overall pictureseems to suggest that among the extensor and flexor muscles of the knee, ankle andback, there is a prevalence for atrophy of the extensor muscles, particularly those ofthe lower limbs.

Whereas common agreement exists regarding this general picture, the time course ofatrophy is less well studied. On the whole, the picture provided by the results of bed-rest studies combined with those obtained by other unloading models, such as lower-limb suspension, suggests that atrophy is described by an exponential time function.As shown in Figure 2.1.4.1, after about 270 days of simulated microgravity, themuscle mass attains a constant value of about 70% of the initial value. Theseconclusions are derived from data obtained on the postural muscles of the calf inhumans, during bed-rest studies lasting a maximum of 120 days withoutcountermeasures. As such, the application of these findings to spaceflight, wherecountermeasures or high-intensity physical activity are undertaken, should bepursued with caution.

Muscle atrophy is the consequence of an imbalance between the rate of proteinsynthesis and degradation. Indeed, during the first two weeks of hind-limb suspension

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Figure 2.1.4.1. Size of the calf muscles (percent of initial value) in humans as a function ofbed-rest duration (days)

Euromir ’94 and ’95 missions on five astronauts have shown that the maximalexplosive power of the lower limbs, as determined during maximal ‘all-out’ pushes ona force platform, was reduced to about 67% after 31 days and to about 45% after 180 days. However, the maximal power developed during 6 – 7 sec ‘all-out’ bouts ona cycle ergometer averaged about 75% of that produced pre-flight. Instead, the musclemass of the lower limbs only decreased by 9 – 13%. Therefore, these data suggest thata large fraction of the decline in the maximal power, at least during the very short‘explosive’ efforts, may be due to the effects of weightlessness on neural drive(involving both supraspinal and spinal reflex activity), the contractile apparatus per se,electromechanical efficiency, and/or muscle damage.

The observation of a disproportionate loss of maximal explosive power compared tothat of muscle mass seems to be a specific characteristic of spaceflight that may notbe easily reproduced by bed rest. Indeed, after 42 days of strict bed rest, the maximalexplosive power was reduced to 77% and the quadriceps’ cross-sectional area to 82%of pre-flight values, indicating that ~95% of the power loss was due to muscleatrophy. When compared to the changes occurring with spaceflight, theseobservations support the hypothesis that the absence of gravity, favouring smoothand delicately balanced muscle actions, brings about a rearrangement of the motorcontrol system. That change is responsible, to a large extent, for the observed declinein the maximal explosive power during ‘all-out’ short-duration muscle actions. Thisrearrangement does not seem to manifest itself so markedly during bed rest, wherethe pull of gravity is not abolished, but simply shifted by 90 ˚.

Besides changes in the functional characteristics of the lower-limb muscles, themechanical properties of tendons are also affected by microgravity. Indeed, a decreasein the stiffness (i.e. the tendon can be stretched more easily) of the series elasticelements of the plantarflexors of the ankle was observed after 1 – 6 months ofspaceflight.

The characteristics of isolated skinned human muscle fibres, obtained from soleusbiopsies performed on four astronauts before and after 17 days of spaceflight, havebeen studied. It was found that a 4% decrease in single fibre specific tension and a30% increase in maximal shortening velocity had occurred. This showed thatmicrogravity tends to favour the slow to fast transition of the soleus muscle fibres, aphenomenon also observed in animals. The increase in shortening velocity wasfunctionally important in compensating for the loss in fibre peak power (~20%), sincewithout the compensation provided by the increased shortening velocity, thereduction in peak power would have been ~34%. For these single fibres, the reductionin peak power was entirely explained by fibre atrophy, because when normalised forchanges in fibre volume the peak power was the same as pre-flight. This is not the casefor the peak power generated by astronauts after prolonged spaceflights of 1 – 6months duration (Euromir ’94 and ’95 missions). This supports the hypothesis that,


2.1.4.3 Functional Alterations

The above structural changes lead to substantial modifications of the muscle function.Indeed, the results of simulation studies on the ground, or during spaceflight onanimal muscles have shown that, whereas the mechanical properties of fast musclesare generally unaffected, those of slow-reacting muscles, such as the soleus, changetowards the fast-muscle type.

For example, in the soleus: (i) the time to peak tension and the half-relaxation time become shorter(ii) the maximal shortening velocity becomes faster(iii) tetanic tension and specific tension (i.e. the ratio of tetanic tension to fibre cross-

sectional area) are usually reduced, because of a decrease in myofibrillar proteinconcentration and an increase in non-contractile tissue.

In contrast, the mechanical characteristics of fast muscles, such as the tibialis anterior,are not greatly affected by simulated microgravity. In addition, the rat soleus muscle,after hind-limb suspension, showed increased fatigability, an increased rate ofglycogen depletion, and a decline in the ability to oxidise long-chain fatty acids. Thisshows that, after hind-limb suspension, the substrate profile of the slow fibres is alsoshifted towards that of fast fibres.

Several studies have reported substantial decreases in muscle strength after bed restor other simulation methods. After 42 days of bed rest, the maximum strength of thelower-limb muscles was decreased by about 30%. No changes in time to peak tension,nor half relaxation time, were found after 17 days of bed rest, whereas under the sameconditions the fatigability and the ratio of tetanic force to cross-sectional areadecreased significantly (8 and 13%, respectively). The observed decrease in the ratiobetween tetanic force and cross-sectional area may be due to:

(a) a reduction in motor drive to the muscle(b) a reduction in fibre specific tension due to a decrease in myofibrillar density(c) a reduction of the ‘efficiency’ of the electro-mechanical coupling(d) an increase in the amount of non-contractile tissue.

After the Skylab missions, the maximal force of several muscle groups (quadriceps,trunk flexors and extensors) showed a decrease from 7 to 25% depending on themuscle group and the flight duration. In addition, since during these missions thecrews performed physical exercise to prevent muscular de-conditioning, the results aredifficult to interpret in terms of underlying muscle fibre function. Data from spaceflightand bed rest show the presence of a disproportionate loss of torque and powercompared to that of muscle size. The decline in maximum power appears to be greaterthan that in maximum voluntary torque. Indeed, data obtained before and after the

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hypertrophy. The magnitude of atrophy of the plantar flexor muscles was similar tothat observed in individuals subjected to unloading only. Altogether, these resultssuggest that resistive exercise may ameliorate, or perhaps even prevent, the negativeeffects of unloading on skeletal muscle.

Penguin-Suit ExerciseThe use of the Russian ‘penguin suit’, an all-body suit with sewn-in elastic bands forthe loading of joints and their related muscles as a countermeasure, has been studiedusing a small group of subjects who were bedridden for about 120 days. The fibre sizeof the soleus muscle was maintained after a single daily 10 h bout of modest loading,i.e. about 10 kg, using the penguin suit to provide elastic resistance. Three subjectswho did not load the ankle-extensor muscles showed soleus atrophy. Although theseresults are encouraging, further research is needed to prove that this technique shouldbe employed in space. There are obvious constraints imposed by the penguin suit, andonboard use of the suit has not produced the desired results.

Drug TreatmentsPharmacological interventions have been considered for preventing or amelioratingmuscle loss due to spaceflight. Experiments on humans, dealing with the issue ofadministering drugs aimed at limiting skeletal muscle protein loss during real orsimulated spaceflight, are not available. However, the impact of albuteroladministration in individuals subjected to 40 days of unilateral lower-limb unloadinghas been examined. In a small subject sample, the efficacy of a resistive exerciseprogramme using flywheel technology to prevent the decline in muscle function wasenhanced by albuterol.

Lower-Body Negative PressureThe application of Lower-Body Negative Pressure (LBNP) alone, or while performingsimultaneous exercise, has been proposed as an in-flight countermeasure. LBNP mayprovide forces, applied to the lower limbs, which simulate weight bearing. It is,however, unlikely that short sequences of such moderate loading would be sufficientto counteract muscle atrophy in space. Although it has been inferred that a regimencomprising LBNP treatment and isokinetic exercise may limit strength loss and musclewasting during bed rest, it is unclear whether LBNP per se contributes to this effect.Thus, the efficacy of LBNP to prevent muscle or strength loss in response to real orsimulated spaceflight remains to be established.

Electrical StimulationTranscutaneous Electromyostimulation (EMS) has been evaluated as an aid to controlmuscle wasting and dysfunction during simulated spaceflight. In a study of threehealthy subjects confined to bed for 30 days, EMS (60 Hz frequency, 0.30 ms pulsewidth, 4 sec train duration) was given twice daily, using a 3-day on and 1-day offregimen. The results showed decreases in strength and muscle mass that were smaller


with increased flight duration, alterations in motor unit recruitment, the contractileapparatus per se, or electromechanical efficiency, and/or the presence of muscledamage may collectively contribute to the decline in explosive power.

2.1.4.4 Countermeasures

- Ground-Based Studies

Aerobic ExerciseResults from a 17-day bed-rest study show that three bouts of progressive cycleergometer exercise until exhaustion, on days 2, 8 and 13, was not sufficient to preventmuscle wasting or a decrease in isometric or dynamic strength of the quadricepsmuscle. This is consistent with other observations. For example, 30 days of bed restinduced a similar effect on knee-extensor strength in individuals who performed cycleergometer exercises for 30 min, 5 days per week, and in controls performing noexercise. Also, daily supine cycle ergometry exercise for 60 min, at 40% of maximumaerobic power, did not prevent muscle or strength loss in individuals subjected to 20days of bed rest. Although in-flight aerobic exercise should be conducted to maintaincardio-vascular functional capacity and the integrity of the aerobic energy machineryand hence endurance, it will not prevent muscle function becoming compromised.

Resistance Exercise Numerous studies have shown that bed rest or unilateral lower-limb suspensionresults in decreased muscle mass or muscle cross-sectional area. This appears to bedue, at least in part, to a decrease in protein synthesis. Healthy subjects who wereconfined to bed for two weeks and performed knee- and ankle-extensor resistanceexercises every other day using a five set, 6 – 10 repetition regimen at about 80% ofmaximum, were able to maintain muscle protein synthesis rate. Subjects who did notperform any training showed a decrease in muscle strength, mass and proteinsynthesis rate. This protocol was also sufficient to maintain dynamic strength; yetisometric strength and neural drive were reduced. While this protocol did notcompletely counteract the reduction in strength, this study provides evidence thatunloaded skeletal muscle benefits from bouts of resistive exercise. It should berecalled, however, that the space analogue intervention lasted no more than twoweeks. In a recent study it was shown that three weeks of unilateral lower-limbunloading produced marked decreases in muscle cross-sectional area and in thestrength of the knee- and ankle-extensor muscle groups. These effects were abolishedby a resistance training regimen consisting of two maximal isometric actions, one setof ten concentric and eccentric actions at 80%, and one set to exhaustion of the one-repetition maximum, performed every third day. Similarly, quadriceps muscle atrophy,induced by five weeks of lower-limb suspension, was prevented by four sets of sevenmaximal concentric and eccentric knee extensions, performed two or three times perweek using flywheel technology. In fact, this regimen produced significant quadriceps

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strength or morphology. This seems to be explained by the fact that a testing protocolcomprised of about 525 contractions (approximately 50% performed at 80 – 100% ofbest effort) was employed on three days during this mission. These results are furtherevidence that high-force muscle actions, and hence resistive exercise, may amelioratethe negative effects of spaceflight on skeletal muscle. Clearly, more research is neededto confirm this, and also to explore the efficacy of different exercise programmes.

2.1.4.5 ‘Explosive’ and Flywheel Ergometers

To prevent muscle loss and function impairment during spaceflight, two innovativeergometers have been proposed: an ‘explosive’ power ergometer and a flywheelergometer. These ergometers allow for the execution of coupled concentric andeccentric actions. Inclusion of both action types in resistive exercise programmes is anessential requirement in order to optimise increases in muscle strength and size.

While exercising on the ‘explosive’ power ergometer (Fig. 2.1.4.2), the subject movesalong a rail on a seat. He or she (and the seat) then accelerates backwards, by exertingan ‘explosive’ push on an approximately equal mass moving on the same rail, but inthe opposite direction. The moving component is fitted with force platforms, so thatthe power exerted by the subject can easily be calculated, provided that the speed ofthe seat and the moving mass are measured. Shock absorbers at the end of the railprovide the necessary braking power. This somewhat cumbersome system minimisesthe shocks and vibrations imparted to the space vehicle. Alternatively, a less bulkysystem, with two astronauts facing each other and accelerating in opposite directions,whilst pushing on a force platform positioned midway between them, could be used.

The flywheel ergometer is equipped with a flywheel that is set in rotary motion (concentricaction) by the subject, throughthe unwinding of a strapanchored to the axle of thewheel and a lever or momentarm, as shown in Figure2.1.4.3. Once the wheel hasbeen set in motion, the samesystem is used to brake it(eccentric action), thus


than in the non-stimulated limb. However, the discomfort associated with EMS, andthe fact that the normal recruitment order of motor units is reversed, make this typeof countermeasure too preliminary to be implemented in space. One solution couldperhaps be to administer EMS in the course of voluntary contractions. This wouldenable the use of physiological discharge rates, thus preventing fibre type conversiondue to chronic stimulation, whilst still producing the high-level contractions necessaryto prevent muscle atrophy.

- Spaceflight Studies

The US and Soviet/Russian space programmes have conducted strengthmeasurements on crews before and after spaceflight. Taken together, these resultsshow that crews suffer from loss of strength, with the effect being most prominent inthe lower limb muscles. The magnitudes of the reported strength decrements showconsiderable variability. However, astronauts also performed in-flight exercise usingdifferent paradigms. On the Euromir ’94 and ’95 missions, the crew exercised for 2 hper day, following a protocol consisting of 1 h of cycle ergometry exercise at brakingpowers from about 100 to about 170 W plus 1 h of treadmill walking. In the latter, aforce provided by bungee cords pulled them towards the ground with an effect equalto about 50% of the their own body weight on Earth.

Unfortunately, on several Shuttle and Euromir missions in the past, countermeasureactivities were not always mandatory nor logged or accurately monitored with regardto frequency, duration or intensity. Therefore, no in-flight exercise programme has yetbeen proved to be effective in preventing loss of muscle and strength during long-termspaceflight.

In-flight Aerobic ExerciseApollo astronauts, who experienced 1/6 g while performing Moon walks, showed nocardiac atrophy upon return to Earth. By contrast, their fellow lunar astronauts, whodid not descend for walks on the lunar surface, did show a decreased heart volumeafter returning to Earth. This may indicate some benefit from physical activity onheart, but not necessarily skeletal, muscle mass in individuals subjected tomicrogravity. In-flight cycle ergometer exercise has been used mainly as an aid tomaintain cardiovascular function. There is, however, no reason to believe that suchexercise will maintain musculo-skeletal function in space, because aerobic exerciseprogrammes typically do not produce muscle hypertrophy at 1g. Preliminary resultsfrom a 17-day spaceflight (STS-78), using a testing protocol identical to that employedin the bed-rest study mentioned above, suggest that it did not prevent muscle wastingor decreases in isometric or dynamic strength of the quadriceps muscle.

In-flight Resistance ExerciseSeventeen days of spaceflight (on STS-78) resulted in minute or no changes in calf

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Figure 2.1.4.2. Schematicrepresentation of the ergometerfor maximal explosive power. FP = force platforms; SA = shockabsorbers; v = velocity (after diPrampero & Antonutto)

2.1.4.7 Conclusions

Skeletal muscle size, structure and function show marked changes followingspaceflight or disuse on Earth. The microgravity environment of space presents aunique opportunity to study true unloading of skeletal muscle. However, because ofthe limited access to this ‘laboratory’ for controlled research studies, paradigms orspace analogues must be extensively used to predict the long-term consequences ofspaceflight on the musculo-skeletalsystem.

Spaceflight results in loss of muscle andimpaired muscle function. Perhaps themost intriguing issue to be solved in thefuture is the observation of adisproportionally greater loss in muscleforce and power than muscle size as aresult of spaceflight or simulatedmicrogravity. The precise role ofmuscular and neural factors should beelucidated in order to fully understandthe causes of this phenomenon, whichmay ultimately impair even the simplestmotor tasks in space and locomotoryactivity upon re-loading in 1g. In thisrespect, the availability of theInternational Space Station (ISS) willenable an extension of presentknowledge regarding the long-termeffects of spaceflight, mainly acquiredthrough the Mir missions. Using state-of-the-art instrumentation, it should nowbe possible to examine a significantnumber of crew members during long-duration missions and under identicaland controlled conditions. Hence, withthe establishment of the ISS as a spacelaboratory, the quality of research in thisfield should be greatly enhanced.

Recently, there has been progress in thedevelopment of techniques and devicesfor preventing loss of muscle anddeteriorated function in space. Whereas


absorbing the flywheel’s kinetic energy, while the strap rewinds. In essence, the flywheelergometer allows the astronaut to perform both positive and negative work. Moreover,the shocks and vibrations imparted to the space vehicle should be easier to control andminimise than those produced by the explosive ergometer. Studies comparing theefficacy of exercise using this ergometer adopted for the leg press and the barbell squatusing free weights, show similar increases in muscle strength for the two methods oftraining over a 12-week period.

2.1.4.6 Cycling in Space

To simulate gravity on a space vehicle, theuse of two mechanically coupled counter-rotating bicycles (Twin Bikes System, TBS),moving at the same speed along the innerwall of a cylindrically shaped spacemodule, has been proposed. The conceptbehind this mode of exercise is thatcircular trajectories induce centrifugalacceleration vectors, oriented in the head-to-foot direction, thereby providingsimultaneous stimuli to the muscular andcardiovascular systems.

The gravitational pull created by thetangential speed at a certain cylinderradius comes close to physiologicalvalues at radii of 6 – 10 m, thus stressingthe exercising muscles as well as thecirculatory system. In addition, thespatial rotation produced by the cyclingaction would produce a potent stimulusto the vestibular system that may proveuseful for the prevention of motionsickness. The results of the head-rotationexperiments performed during theNeurolab mission seem to confirm theimportance of training the vestibularsystem. Combining high-intensityexercise and simulated gravity mayprove useful for simultaneouslyameliorating muscle atrophy, bonedemineralisation and cardiovascular de-conditioning.

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Figure 2.1.4.3 (a) The principle of theflywheel ergometer. The force generatedduring concentric muscle action increasesthe flywheel’s rotation and stores kineticenergy in the spinning wheel. An eccentricmuscle action is then performed to slowdown the flywheel. (b) A multi-exerciseconfiguration of the flywheel ergometer.The device is equipped with a seat thatcan be either fixed, allowing for e.g. upperbody exercise, or sliding while performingthe dead-lift, the heel raise, the leg press orthe squat. The seated-leg-press exercise isshown here

Figure 2.1.4.4. Upper panel: cyclistsmoving along the inner wall of acylindrically shaped space modulegenerate an acceleration vector mimickinggravity. Lower panel: Schematic of the TwinBikes System, with thick lines indicatingspace-module walls. The differential gearcoupling is drawn on a larger scale andthe adjustable masses are also shown(after di Prampero & Antonutto)

(a)

(b)

2.1.5 The Skeletal System

R. Cancedda

2.1.5.1 Bone Remodelling, a Lifelong Process

During embryo development, bone is formed either directly, starting from anundifferentiated embryonic tissue, or via ossification of cartilaginous tissue. Afterbirth, and until sexual maturity, bone formation via this cartilaginous model persistsin the growth plate of long bones and plays a major role in their development.

Bone density undergoes physiological changes throughout life. An acquisition phaseoccurs during childhood and adolescence, with the peak bone mass being reached inthe mid- to late-twenties. Bone density then changes very little for several years, as itgoes through a ‘plateau phase’. A period of bone loss then follows, which startsaround the age of 50. In the following 20 to 30 years, bone density decreases byapproximately 15% in men and 30% in women. Under normal conditions, thisprogressive bone-mass reduction does not impair the quality of the bone’s supportproperties.

Throughout life, bones are continuously remodelled as a result of the coupledactivities of bone resorption and formation. In this process, tiny pieces of old bone arecontinuously replaced by new material. By this means, spatial changes in form canalso be brought about. The bone resorption is a process carried out by specialised cellscalled osteoclasts. In the body, osteoclasts form as the result of the transformationand fusion of specific white blood cells. Bone formation is the result of the activity ofother specialised cells, called osteoblasts.

When new bone is needed, new osteoblasts are formed as consequence of an increasein the number (proliferation) and the transformation (differentiation) of a fewprogenitor cells, located in the bone marrow. Newly formed osteoblasts localise in thearea where old bone has been removed. Here they produce and secrete severalproteins outside the cell. These proteins form a mesh, filling all of the space betweenthe osteoblasts. Calcium mineral is deposited within this protein mesh. In this way,new bone is formed and old bone replaced. The replacement of old bone may beinduced due to an insufficient number of blood vessels being present and the fact thatthe bone is no longer responding to the changing mechanical requirements of thebody.


medium-intensity cycling exercise may be effective in counteracting cardiovascularde-conditioning, high-intensity muscle loading by resistive and/or explosive exerciseseems particularly promising for the prevention of muscle atrophy and weakness inspace. Integration of the results on muscle atrophy and functional changes in spacewith those of disuse muscle atrophy and sarcopenia on Earth will certainly enhanceour understanding of the physiological and pathological mechanisms that lead to lossof muscle and altered function. Knowledge of these mechanisms will be extremelyuseful for designing better strategies for counteracting muscle de-conditioning due toneuromuscular diseases, traumatic injuries and ageing.

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from a fracture of the hip, wrist or vertebra. The risk of fractures for the malepopulation of the same age is about 12 – 15%.

Osteoporosis can be defined as a reduction in skeletal mass, associated with bonemicro-architectural deterioration, which results in an increased risk of fractures. It canbe a debilitating disease, with devastating health and economic consequences.Osteoporosis occurs when the body fails to form enough new bone and/or when toomuch bone is reabsorbed. This bone loss occurs over several years and usually afracture of vertebrae, wrists, or hips is the first sign of a pathology of which the patientwas not aware. At the time of the first fracture, the disease has usually already reachedan advanced stage and other serious symptoms soon occur. These include pain in thelower back, neck pain, bone pain and tenderness, loss of height over time and,eventually, a stooped posture.

2.1.5.2 The Effect of Mechanical Stress on Bone

Mechanical loading is essential for the maintenance of skeletal structure, and areduction in mechanical loading leads to rapid bone loss. A serious loss of bone mass(and structural mechanical efficiency) is induced by complete immobilisation or byweightlessness, regardless of a normal healthy condition of the endocrine systems.

For example, in hind-limb-unloaded rats, an acute decrease in bone formation isobserved at the end of the first week. This is due to a reduction in the number of bone-marrow progenitor cells, from which osteoblasts are derived, and an increase in boneresorption, leading to the net bone loss. At six weeks, significant bone loss associatedwith an altered bone structure was observed, and as a consequence a decrease in theskeletal structural strength also. After reloading, a rebound in bone formation wasalways observed, but the recovery time was longer than the duration of the limbunloading. In all cases, bone-massrecovery was never complete.


In general, certain hormones circulating in the blood have effects on the wholeskeleton, by controlling the number of active osteoclasts and osteoblasts, whereas‘local factors’ have effects mainly in the skeletal area where they are released. Theselocal factors are synthesised by skeletal and adjacent cells and include growth andmorpho-genetic forming factors. Growth factors may have effects on the cells of thesame class that have synthesised and released them, or on other cells within the sametissue. Circulating hormones may act on skeletal cells either directly or indirectly, bymodulating synthesis, activation, receptor binding, and binding properties of localgrowth factors.

Among the hormones with specific effects on bone, oestrogen merits a specialmention. Oestrogen depletion at the female menopause can induce bone loss byaltering osteoblast bone-formation activity, which in turn leads to unregulated boneremodelling and, potentially, to osteoporosis.

Osteoporosis is the principal bone disease in Europe and in the USA. It has variouspotential causes in addition to the prime cause, which follows the reduction inoestrogen due to loss of ovarian function in post-menopausal women. The otherpotential causes include endocrinological disorders, such as corticosteroid excess(Cushing’s syndrome), hyper-thyroidism, and hyper-parathyroidism. Other causes areimmobilisation, bone malignancies, some genetic diseases, a low amount of calciumin the diet, eating disorders, heavy alcohol consumption, smoking, and the use ofcertain drugs, such as steroids.

It is also common knowledge that there is a genetic predisposition to osteoporosis,although the basis for this is still unclear. White and Asian women are at higher risk.It is estimated that almost 25% of all women over the age of 50 have osteoporosis,and about 50% have osteopenia, a low-bone-density situation that may eventuallyresult in osteoporosis. It is expected that more than 50% of women over 50 will suffer

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Figure 2.1.5.1. Bones are continuouslyremodelled as a result of the coupledprocesses of bone removal by osteoclastsand bone formation by osteoblasts. Withageing, bone loss prevails both in men andwomen, although the bone-mass decreaseis much more dramatic in women. Undernormal conditions, the progressivereduction in bone mass does not impairthe bone’s mechanical properties.Osteoporosis is characterised by anextreme reduction in skeletal mass,associated with bone micro-architecturaldeterioration, which results in anincreased risk of fractures (modified from:www.osteovision.ch)

Figure 2.1.5.2. Significant bone loss occursas a consequence of unloading ormicrogravity exposure. The upper panelsare micro-radiographs of transversalsections of loaded and unloaded longbones. The lower panels are longitudinalsections of the shin bones (tibiae) of a rat,which remained in space for 1 week duringthe Cosmos-1667 mission, compared to acontrol rat that remained on the ground.Note the reduced amount of bone internalorganisation (bone trabeculae). BT = bonetrabeculae; cart = growth plate cartilage(courtesy of A. Zallone and L. Vico)

As yet, the mechanisms underlying the observed bone loss in space are only partlyunderstood. In this respect, it is worth noting that several endocrine systems undergochanges in space that resemble those observed during senescence. This appears to beparticularly true for the systems regulating bone metabolism and turnover.

2.1.5.4 Microgravity and Osteoporosis Research

Space travel and the extension of the average human life span are two of the majoradvances during the last century. However, at present, the price that has to be paid for bothof these advances lies in the progressive degradation of normal physiological processes.

Both old age and prolonged exposure to microgravity conditions are associated withdecreased bone mass and damaged bone structure. In the latter case, however, thechanges occur at a greatly accelerated rate and in healthy individuals. Consequently,it has been suggested that careful experimentation in microgravity could represent agood basis for investigating the mechanisms responsible for bone loss in old age, andthe occurrence of osteoporosis. Those investigations need to consider mechanismsoperating both at the cellular and at the whole organism level.

Therefore, a major long-term objective of future space research in osteobiology will beto provide new tools for both the treatment and the prevention of bone diseases suchas osteoporosis. That will require an integrated understanding of their underlyingcauses, including genetic mechanisms. The research should take advantage of thetremendous progress made in the last decade in the cell-biology field. Animal-basedresearch should also be used to test promising interventions, taking advantage of theaccelerated bone-loss process in microgravity, which offers an excellent tool for suchstudies. The final goal then is to expand the transfer of the new knowledge acquiredthrough space research directly to diagnostic, therapeutic, and preventiveapplications of potential benefit to an ageing world population.

- Cell and Tissue Cultures

The basic mechanisms that control bone cell division, activity and death may besimilarly altered in both the elderly and individuals exposed to microgravityconditions. The changes observed in bone formation could be, at least partly, theresult of a decreased osteoblast activity, resulting in decreased extra-cellular proteinmatrix deposition and mineralisation. A possible explanation may be that theosteoblasts themselves are sensitive to altered gravity levels, as suggested by severalstudies in which the effect of microgravity on osteoblasts cultured in space wasinvestigated (see Section 2.2.1).

Few studies have been performed to examine the effects of microgravity exposure onexplanted developing skeletal tissues. Embryonic cartilaginous mouse bones were


In human bed-rest experiments, volunteers are immobilised by a plaster cast fromtheir waist to their toes. Progressive loss of mineral from bone, together with anincrease in calcium excretion, was observed during the first four weeks. The calciumloss continued in the following weeks. At the end of a seven-week experiment, theaverage calcium loss was shown to be about 0.5% per month.

When bone loss was examined by measuring bone-mineral densities (a measure ofbone quality) at specific locations, such as in the forearm (radius) and the heelbone(calcaneus), major differences were observed. In general, demineralisation wasmuch higher in weight-bearing bones. For example, the central area of the heel bone canhave lost up to 45% of its mineral mass after seven months of immobilisation.

2.1.5.3 Bone Loss in Space

The first observation of an increase in the level of urinary calcium was made in 1962,during the short flights of Vostok-III and IV. Since then, a series of reports have beenpublished on modifications of calcium balance, alteration of bone-mineral density andbone turnover, observed in astronauts and cosmonauts who have stayed in space forvarious lengths of time.

The first data concerning bone loss during long-duration missions came from theSoviet/Russian missions. A significant loss at the heel bone was found after missionslasting 75 to 184 days, with the loss roughly proportional to the flight duration.Quantitative computerised tomo-densitometry (QCT) was used to determineperipheral (cortical) and central (trabecular) bone mass at different skeletal sites in twocosmonauts, who were in space for 1 month and 6 months, respectively, during theEuromir ’94 and ’95 missions. Weight-bearing bones were observed to be moreaffected by microgravity than non-weight-bearing ones. It is notable that, six monthsafter landing, recovery was still not complete in the central area of the bones, which ischaracterised by a high remodelling rate, whereas the peripheral bone, characterisedby a lower remodelling rate, had recovered to pre-flight levels.

So far, the published data have related to a limited number of cosmonauts and highindividual variations were observed. Recently, bone-mineral density measurements atboth the forearm (radius) and shin bone (tibia) have been reported for 15 cosmonautsvisiting the Russian Mir space station. They had stayed in space for either one (2cosmonauts), two (2 cosmonauts), or six (11 cosmonauts) months . After a recoveryperiod comparable in duration to that of the relevant space mission, forearm bonedensity had not changed significantly. In contrast, the weight-bearing shin bone,despite the physical training of cosmonauts during space missions, still showedevidence of central bone loss after one month of recovery, and of peripheral bone lossafter two months of recovery. Observed shin-bone deterioration continued to increasewith flight duration.

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The results of these studies were limited by a number of poorly controlled factors,including the strains and ages of the animals and the type of restraining device.Nevertheless, some general conclusions and a catalogue of events could be derived.

An alteration in the internal organisation of bone was found to have occurred by theend of the first week. After the second week, clear evidence of bone loss was observed,mostly due to an abrupt and transient increase in bone resorption. After the thirdweek, a net decrease in bone formation was also observed. In all of the casesinvestigated, recovery of bone formation occurred after return to Earth, although thedecreased internal bone organisation often persisted. Investigations of the molecularmechanisms underlying the bone cellular alterations have just been started.

A few Russian experiments have involved monkeys. A two-week space flight wasfound to have induced a severe bone loss in the primate iliac bone, as well as adecrease in mineralisation activity and an altered mineralisation pattern.

- Animal Models for the Study of Bone Development and Turnover

Osteoporosis is characterised by a decrease in bone mass and a concomitant increasein the propensity for bone fractures. There are numerous risk factors for osteoporosis.Although many of them are non-genetic in nature, there is a definite geneticcomponent as well. Genetic control of osteoporosis depends upon several genes, andthe specific genes involved are just beginning to be identified.


cultured during three Space Shuttle flights, to study cartilage growth, thedifferentiation to form bone and the process of mineralisation in a microgravityenvironment. The bones cultured in microgravity grew less in length than the groundcontrols. In addition, the amount of calcium incorporated into the mineralised areaswas significantly lower. This suggests that the composition or density of themineralised regions was compromised in microgravity.

- Animal Studies

So far, the rat has been the animal most widely used for spaceflight studies. Bonemeasurements have been performed on growing rats returning from 4 to 21-day spaceflights (see Table 2.1.5.1).

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Table 2.1.5.1. Studies of rat bones in space (courtesy of L. Vico)

Space flights Rat type Weight (g) at Time betweenlaunch (L) or death (D) landing and

sacrifice (h)

1973 Cosmos-605; 21.5 days Unknown Unknown 48, + recovery

1975 Cosmos-782; 20.5 days Wistar 215 (L) 72, + recovery

1977 Cosmos-936; 19.5 days Wistar 202 13.9 (L) Unknown, + recovery

1979 Cosmos-1129; 18.5 days Wistar 349 ± 4 (D) 7 – 11, + recovery

1983 Cosmos-1514; 5 days Wistar, 293 ± 6.5 (D) over 6pregnant

1985 Cosmos-1667; 7 daysWistar 304 ± 46 (D) over 6

1987 Cosmos-1887; 12.5 days Wistar 303 ± 2 (D) 42 – 55

1989 Cosmos-2044; 14 days Wistar 338 ± 2 (D) 6 – 10

1985 SL-53; 7 days Sprague-Dawley Large 384 ± 9 (D) 11 – 17Small 194 ± 10 (D)

1993 SLS2; 14 days Sprague-Dawley Around 330 (D) 5 – 6, + recovery

1993 STS-54; 6 days Sprague-Dawley 210 – 223 (D) 6 – 13

1990 PSE-1 (STS-41); 4 days Sprague-Dawley 120 (L) 4 – 6

1992 PSE-2 (STS-S2); 10 days Sprague-Dawley 180 (L) 5 – 3

1993 STS-58 (SLS2); 14 days Sprague-Dawley 251±10 (L) 2–3 or 14 days of recovery

1995 STS-62; 14 days Fisher 344, about 140 (L) 4 – 6ovariectomised

1996 STS-78; 17 days Sprague-Dawley about 165 4 – 7

Figure 2.1.5.3. The obese mouse: an example of gene mutation affecting bone mass.Mutations in the obese (ob) gene lead to major metabolic changes in mice. In addition toobesity, diabetes and other alterations, an increased bone mass is also observed (fromNature1994, 372, pp. 425 – 432)

2.1.5.5 Conclusions and Future Research

Throughout life, bones are continuously being remodelled as a result of the coupledbone-resorption and bone-formation activities, which substitute tiny pieces of oldbone in both the central area and within peripheral cortical bone. When these twoactivities cease to be in dynamic equilibrium, excess bone may be reabsorbed and/orinsufficient new bone is generated. The resulting deficit can lead to osteoporosis. Thisis characterised by a reduction in the skeletal mass, with an associated deteriorationin the bone micro-architecture. The consequence is an increased risk of fractures andskeletal deformation. It can be a debilitating disease, with devastating health andeconomic consequences.

Microgravity conditions affect the skeleton and induce bone loss in both humans andanimals. During spaceflight, bone is lost principally from the bones that are mostloaded by gravity when on Earth. Bed-rest studies with human volunteers and hind-limb elevation studies with animals still provide useful data to help explain some ofthe changes occurring. Nevertheless, microgravity exposure represents the onlysituation whereby the absence of gravity acting on the entire body can be used as atool.

Studies of skeletal unloading, particularly during microgravity exposure, will provideinformation that could improve our knowledge of the mechanisms controlling bone-mineral deposition and loss. Such understanding will lead not only to measures forpreventing defective bone formation and bone loss during future long-duration spaceflights, but will also assist in developing cures for human osteoporosis. Themechanisms involved in these alterations need to be investigated at the cellular andmolecular levels, and at the level of the whole organism.

The data available on the effects of mechanical stress and of microgravity on bonecells suggest that some of these cells may respond to stress and to unloading ‘in vitro’.However, at this stage these data should be treated with caution, due to the numerouslimitations related to the methods used and to the limited number of studiesperformed to date, especially in space.

So far, ESA has never carried out animal research in space. Some European scientistshave performed experiments on animals, mainly rats, through bilateral agreementswith the USA and Russia. The results obtained have shown the value and relevance ofanimal studies in creating the link between cell biology and human physiology. This isparticularly true in the case of bone research.

The present availability of ‘transgenic’ and gene ‘knock-out’ mouse mutants, in whichparticular genes responsible for bone development and remodelling have beenmodified or deactivated, will be particularly useful for understanding the genetic


The possibility of manipulating the mouse genoma and of introducing mutations inspecific genes is one of the most important advances in modern molecular genetics.This technology has increased the number of mutant vertebrate organisms that areavailable. It is becoming the main research tool directed to determining the potentialactivities of the new genes discovered via the human genome sequence (genomic-functional analysis).

The technologies available today permit animals to be created in whose genoma eitheradditional copies of certain genes (transgenic genes) are introduced, or specific genesare deactivated (knock-out genes). In recent years, several ‘transgenic’ and ‘knock-out’mice have been created that mimic human bone and cartilage pathologies, and inwhich a particular gene responsible for bone development and remodelling has beendeactivated. Such transgenic and knock-out mice have been very useful in studyingrare and lethal skeletal diseases. It was also possible to create strains of micegenetically predisposed to degenerative skeletal disorders. Studies on the transgenicand knock-out phenotype of these mice, maintained in various experimentalconditions, including microgravity, will generate new information on the mechanismsthat control bone formation and turnover, both in normal and in pathologicalsituations such as osteoporosis.

- The Development of Countermeasures

All astronauts are required to devote several hours per day to physical exercise. Theincrease in muscle activity can influence bone formation positively, but so far it is onlypartially effective in preventing bone loss.

The mechanisms of bone loss in space are only partially understood. Consequently,the development of practical measures that are able to counteract space-induced boneloss is presently a high priority for scientists involved in bone research. High dietarycalcium increases bone mass and mineral content in animal-model unloaded bones,but fails to prevent a decrease in bone mass compared to control (loaded) animalssubjected to the same diet. Treatment with hormones and growth factors, known toplay a role in bone formation and turnover, only partially prevents the bone lossinduced by skeletal unloading. Administering drugs, such as bisphosphonates, thatare potent inhibitors of bone resorption and are currently used for the treatment ofhuman osteoporosis, does reduce the trabecular bone loss in the unloaded bones, butit also results in an alteration of the bone structure.

Therefore, none of these procedures and treatments can be considered fullysatisfactory and additional studies are required. This appears all the more importantbecause it is expected that, when the International Space Station is fully operational,many astronauts will remain in space for several months at a time.

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2.1.6 The Human Sensory and Balance System

G. Clément


Andrew Thomas, an astronaut who spent 141 days on Mir in 1998 describes what itwas like to return to Earth after some five months in zero gravity. “I landed lying onmy back and reached for my camera – it felt amazingly heavy, like a huge fifty-poundlead dumbbell”, he recalled. He was overcome by vertigo, and – when he was helpedto his feet and supported on both sides by the ground crew – by gravity too. “It wasincredible. Just putting one foot in front of the other required tremendous effort.” Hisbalance was poor, and he staggered forward, listing to the side. Over the next fewdays, he recounts, “I had to walk slowly with a wide-based gait. Fine balance skillstook several weeks to return. When I walked with my eyes closed, I still veered to theside and walked into the wall.” Thomas underwent many weeks of rehabilitation, asis standard practice, with graduated exercises, guided movements in a warmswimming pool, and massage. Even after a month, however, he couldn’t jog withoutbecoming short of breath.

Balance disorders have also beendescribed even after shorter spaceflights, such as one-week space missionsaboard the Space Shuttle. Troublesreported include the sensation that thevisual environment moves when theastronauts make a rapid head motion,feeling that the ground is bobbing whilststepping, an inability to walk in astraight line with eyes closed, and loss oforientation when riding in a vehicle orwalking in the dark.

Obviously, these changes indicate thatsome form of adaptation by the centralnervous system to the loss of gravitational information takes place during space flight.This adaptation then carries over in a detrimental way to the post-flight period. In thisSection, the way in which experiments performed during space flight can be used toenhance our understanding of the human sensory and balance system will bereviewed.


component of both bone loss in space and osteoporosis. Hopefully, the informationacquired will allow the development of countermeasures for astronauts on futurespace flights, as well as for the global prevention and treatment of osteoporosis.

Further Reading

Bianco P., Cancedda D., Riminucci F. & Cancedda R. 1998, Bone formation via cartilagemodels: the ‘bordeline’ chondrocyte, Matrix Biol., 17, pp. 185 – 92.

Marie P.J. 1998, Osteoblasts and bone formation. In: Advances in Organ Biology:Molecular and Cellular Biology of Bone (Ed. M. Zaidi), JAI Press, USA., 5B, pp. 401 –427.

Marie P.J., Jones D., Vico L., Zallone A., Hinsenkamp M. & Cancedda R. 2000,Osteobiology, strain and microgravity. Part I: Studies at the cellular level, Calcif. TissueInt., 67, pp. 2 – 9.

Rodan G.A. 1996, Coupling of bone resorption and formation during bone remodelling.In: Osteoporisis (Eds. R. Marcus, D. Feldman & J. Kelsey), Academic, San Diego, pp. 289 – 299.

Vico L., Collet P., Guignandon A., Lafage-Proust M.H., Thomas T., Rehaillia M. &Alexandre C. 2000, Effects of long-term microgravity exposure on cancellous andcortical weight-bearing bones of cosmonauts, Lancet, 335, pp.1607 – 1611.

Vico L., Hinsenkamp M., Jones D., Marie P.J., Zallone A. & Cancedda R. 2000,Osteobiology, strain and microgravity. Part II: Studies at the tissue level, Calcif. TissueInt. (in press).

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Figure 2.1.6.1. French astronaut Jean-PierreHaigneré after his return to Earth followingnearly six months in the weightlessconditions of space

lowering the whole body in space with the feet anchored can evoke illusions of deckdisplacement. The floor seems to move upwards as the body moves towards it, anddownwards as the body moves away from it. These illusions probably result from thealtered relationship between the motion of the body, the muscle forces necessary toproduce that motion, and the associated spindle feedback from the muscles.

Lifting and manipulating objects is also an important aspect of limb movementcontrol. Studies of the ability to discriminate differences in the masses of objects ofsimilar size and appearance by hefting them show a degradation of performance inweightless conditions. If the hefting frequency is increased, performance improvesconsiderably. Rapid arm movements are known to be less dependent for theiraccurate execution on muscle spindle feedback and are less impaired than slowmovements during space flight. Consequently, the degradation in mass discriminationassociated with slow movements is likely to reflect errors in resolution of limbtrajectory, at least in part. Subjects experience post-flight increases in the apparentheaviness of hefted objects and of the body and limbs. This change points to areinterpretation by the central nervous system of the apparent effort associated withsupporting the limbs or holding objects against gravity.

Our sixth sense, the sense of motion, is mediated by the vestibular system. The innerear contains two balance-sensing organs, both of which are designed to keep theindividual upright, orientated, and moving smoothly. One organ, comprised of thesaccule and utricle, sends messages to the brain as to how the head is positionedrelative to the force of gravity (Fig. 2.1.6.3). The saccule and utricle are tiny sacs, linedwith hair cells. Small calcium-carbonate particles, the otoliths, rest on these hair cells.When the head moves relative to gravity, the weight and movement of these otolithsstimulate the hair cells and give the brain information on ‘up’, ‘down’, ‘tilt’ and‘translation’ in a particular direction. The other balance-sensing organ is comprised ofthree semicircular canals. It provides the brain with information on rotation about thethree axes of yaw, pitch and roll.

These two balance- and motion-sensing organs form the vestibular apparatus. Thelatter is connected to several other key systems involved with balance, orientation,

and movement. Informationtravels from the vestibularsystem to the eyes, to keepthem focused on a target


2.1.6.2 Adaptation of Human Sensory Systems to Weightlessness

Human sensory functions are classically categorised into five areas: hearing, taste,smell, vision, and touch. Neither the hearing function, nor the ability to localise soundsources, is altered in weightlessness. Slight changes in taste, smell, and vision wereobserved during space flight, but these changes were indirect effects ofweightlessness, in which the system responds not to the gravitational force itself, butrather to changes in the local environment induced by conditions of weightlessness.For example, the changes in the taste and smell of food reported by some crewmembers are more likely to be related to the reduction in air convection inweightlessness. Also, the fact that 10 – 20% more stars are visible from space in lowEarth orbit and that the objects outside the spacecraft appear ‘unreal in clarity’, asreported by the first astronauts, are presumably due to the absence of light scatteringin vacuum. The unusual colour and shading contrasts encountered on the Moon, aswell as the absence of objects with familiar sizes in the background (such as trees,people, vehicles, etc.), were presumably responsible for the impairment of theastronauts’ ability to judge distances on the Moon.

Position sensing, or limb proprioception, is derived from afferent signals of the musclespindles and receptors situated in tendons and joints, which are interpreted in relationto ongoing patterns of muscle activity. On Earth, muscle spindle sensitivity is influencedby head orientation, which is detected by the otolith organs in the vestibular systemand modulates the antigravity muscles of the body through spinal-cord connections.

The astronauts frequently report that limb position sensing is degraded in weightlessconditions, and this is confirmed byexperiments in which they have to pointto visual targets without seeing their arm.

Scientists believe that this degradation isdue to a change in the perceptualinterpretation of proprioceptive signals,rather than a decrease in muscle spindlesensitivity. Indeed, on the groundvibration of leg muscles of a test subjectrestrained in the standing position leadsto illusory tilting of the body. Duringspace flight, such vibration leads to thesensation that the deck, to which theastronaut is attached with foot supports,is tilting or rising under his/her feet,depending on the muscles stimulated.Similarly, deep knee bends or raising and

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Figure 2.1.6.2. The Pointing Experiment on the Neurolab STS-90 mission, in whichthe astronaut tracked a moving targetdisplayed on the device’s screen. The circleof light shows the track that he made withhis hand

Figure 2.1.6.3. The humanbalance system, its location withinthe inner ear (left) and itsconnections with other keysystems involved with balance,orientation, and movement (right)

patterns in the frontal plane, the astronauts experience full 360° roll self-motion, areaction that happens rarely on Earth. This enhanced effectiveness of visual stimuli forinducing apparent self-motion is probably also responsible for the illusion of ‘feelingupside down’ when the astronauts’ feet point to the spacecraft’s ceiling. There arelarge differences between individuals though. For some astronauts, for example, thedirection in which their feet point is always ‘down’, and changing their bodyorientation within the space vehicle does not shift the apparent ‘down’ direction.

On the Earth’s surface, gravity significantly affects most of our motor behaviour. It hasbeen estimated that about 60% of our musculature is devoted to opposing gravity. Forexample, when making limb movements in static balance, anticipatory innervationsof leg muscles compensate for the impending reaction torques and the changes inlocation and projection of the centre of mass associated with these movements.Similar patterns of anticipatory compensation are seen in-flight, although they arefunctionally unnecessary. Also, rapidly bending the trunk forwards and backwards atthe waist is accompanied on Earth by backward and forward displacements of thehips and knees to maintain balance. The same compensatory movements of hips andknees are made in weightlessness. Since the effective gravity torques are absentduring space flight, the innervations necessary to achieve these synergies inweightlessness are different from those needed on Earth. Consequently, these in-flightmovements must reflect reorganised patterns of muscle activation.

Locomotion in the absence of effective gravity is quickly learned by the astronauts. Onthe other hand, post-flight posture and locomotion disturbances are commonplace.Static posture exhibits a considerable increase in sway amplitude, especially in theabsence of visual and proprioceptive cues. The phases of the step cycle, duringlocomotion, show serious post-flight alterations, and the head is more unstable. Thesealterations are also presumably the consequence of adaptive changes in the centralnervous system to the control of posture and movements during space flight. Fullrecovery can take weeks, even after short space missions. Systematic quantitativemeasurements of posture and locomotion after long missions are presently lacking.

During head movements, the vestibular apparatus transduces head velocity andrelays this information to those centres controlling eye position to generatecompensatory eye movements; this reflex behaviour ensures that vision is not blurred.When performed in darkness, this leads to a pattern of rhythmic eye movementsknown as nystagmus, consisting of slow phases in the direction opposite to the headand fast phases that bring the eye back when it reaches the extreme of its travel. Thenystagmus response to a rapid head movement outlasts the changes in signals in thesemicircular canals, through the activation of a velocity storage mechanism located inthe brain stem. This so-called ‘vestibulo-ocular reflex’ has been studied systematicallyin orbital flight, both during active (voluntary) (Fig. 2.1.6.5) and passive headmovements (Fig. 2.1.6.6). The basic finding is that gravity has no influence on


whilst the body is moving. The hippocampus also uses information from the inner ear,which is important for knowing locations and navigating. Nerves travelling from thevestibular system to the cerebellum help produce precise, smooth and co-ordinatedmovements. Vestibular information travels down the spinal cord to the muscles, tomaintain balance and posture.

The question is whether the part of the vestibular system that is sensitive to gravitycontinues to operate in weightlessness. Head tilt is not sensed by the otoliths in theabsence of gravitational force, but they are still activated by the inertial force oftranslational motion. Experiments performed in space to date, including those usingthe ESA 4 m-long Sled moving with very low accelerations, have not shown significantchanges in sensitivity to linear acceleration during and after space flight. Since thebrain receives inputs from the otoliths only when there is a translational head motionin weightlessness, it has been proposed that the brain re-interprets tilt-related otolithinformation as translation during space flight. This has been the theoretical basis ofmuch space research for the last 15 years. Only recently has this hypothesis actuallybeen tested, using a centrifuge installed onboard the Space Shuttle.

However, the vestibular system rarely works alone. Vestibular inputs are generallycombined with visual, proprioceptive (stretch), and tactile (touch) inputs for theperception of self-orientation and motion. These multi-modal sensory stimuli are alsocompared with motor feedback inputs for the appreciation and regulation of bodyorientation. This sensori-motor integration (often referred to as the neurosensorysystem) plays a key role in posture and movement control, locomotion, and objectmanipulation in a gravitational environment. During the last 20 years, extensiveexperimental research has been performed to investigate the effects of weightlessnesson the mechanisms of spatial orientation, postural control, hand – eye – head

coordination, and spacemotion sickness.

Space experiments have shownnicely that visual cues alonecan provide a sense of self-motion and tilt. Whenpresented with rotating visual

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Figure 2.1.6.4. The ESA Space Sled,used on the German D-1 Spacelabmission. Providing linearaccelerations along all body axes, it was used to evaluate possiblechanges in the detection threshold for very low linear accelerations inspace

to provide a reference for ‘down’ or ‘up’, the basis for orientation shifts to an internallygenerated reference. Thus, the ‘down/up’ vector is now perceived as being alignedwith the longitudinal axis of the body. However, further experiments in space involvingsimultaneous recording of body posture, oculomotor responses, subjective illusionsand motion-sickness symptoms are required to test this hypothesis.

2.1.6.3 Development of the Vestibular System

Since life first appeared on Earth, gravity has been a constant selective force.Consequently, the development and behaviour of all organisms have gravity as anindirect, if not direct, determinant. In many cases, the role of gravity in biologicalprocesses can be revealed explicitly under weightless conditions.

During gestation and early development, there is a fixed sequence in which sensorysystems achieve an onset of function, i.e. when a sensory system begins to respond tostimulation, such as the visual system to light, the olfactory system to odours, thevestibular system to linear or angular acceleration, etc. In every vertebrate speciesthat has been examined so far, the onset of function occurs in the following sequence:tactile, vestibular, auditory, visual. Interestingly, in all species the onset of vestibularfunction occurs prior to hatching or birth, in contrast to hearing or vision, which canbe post-natal in some species. This means that the foetus is potentially susceptible tovestibular stimulation in its pre-natal environment. Mammalian offspring emerge fromthe birth canal in a species-typical orientation that, for rats and humans, is head-first.Foetuses typically achieve the appropriate orientation via active, in-utero behaviour. Itwould appear that the vestibular system is employed for this early task. Indeed, manyinfants born in the breach position are born with vestibular disorders. Also, the so-called ‘righting response’, by which newly born mammals actively adjust from asupine to a prone position, is disrupted by induced vestibular disorders duringdevelopment.

In the development of the visual system, activity in the retinal pathway influences thespecification of those connections that determine how visual information is processedin the cerebral cortex. In every other sensory system known, especially those thatmake up the neural space maps in the brain stem, sensory stimulation has beenimplicated in the initial specifications of the connections and physiological propertiesof the constituent neurons. Only in the otolithic gravitational pathway has it beenimpossible to study the role of sensory deprivation, because there is no way to deprivethe system of gravitational stimulation on Earth.

For this reason, experiments in microgravity should be planned to test the hypothesisthat gravity itself plays a role in the development and maintenance of the componentsof the vestibular system. These components include both the vestibular receptors ofgravity – i.e. the sensory hair cells in the utricle and saccule, vestibular ganglion cells


Figure 2.1.6.6. (a) The hand-spun rotating chair, used during the SLS-1 mission. (b) Theservo-controlled rotating chair used during the IML-1 mission, shown here in the pitchorientation

the peak slow phase velocity ofthe nystagmus, elicited by rapidyaw or pitch head movements.However, the time constant ofnystagmus decay is shorterduring space flight than onEarth. Interestingly, on Earthwhen the otolith organs areablated, velocity storage is alsodiminished. The data obtainedin weightlessness were the first evidence that the velocity-storage mechanism issensitive to linear acceleration.

Humans sense gravity on Earth directly through receptors in the inner ear andindirectly by touch and stretch. In space, the central nervous system interprets theinputs from these receptors differently. In the first few days of space flight, about halfof the astronauts experience a type of motion sickness. This seems to be due to theabsence of the constant input from those sensors in the inner ear, the otolith organs,which sense linear acceleration and gravity. In this period, the astronauts areparticularly sensitive to tilting of their head to the side, front or back, and theyfrequently hold their head and neck very stiffly. The basis for this space motionsickness appears to be that the brain no longer receives an input that signals that thehead has moved relative to gravity. After several days in weightlessness, theneurosensory system adapts to the new situation; the symptoms relapse and headmovements no longer produce nausea. It is believed that at this point the referenceframe for spatial orientation has changed. Since one can no longer depend on gravity

(a) (b)

Figure 2.1.6.5. Subject participating inan experiment to measure eye reflex

movements during voluntary headmotion (COIS experiment, STS-78)

2.1.6.4 What Exactly has been Learnt from Microgravity Experiments?

A few examples are reported here of space experiments that have provided valuableresults that could not have been obtained under terrestrial conditions.

- The Caloric Nystagmus is not due solely to Thermal Convection

The most widely used clinical check on the functioning of the vestibular system is thecaloric test. During this test, irrigation of the external auditory ear with water or airabove or below body temperature generates, by thermal conduction, a temperaturegradient across the inner ear. As a result, the vestibulo-ocular reflex (see above) istriggered, producing characteristicrhythmic eye movements (nystagmus)and the subject experiences slightvertigo. For many years it was generallybelieved that this response was initiatedby the differences in specific gravity ofthe inner ear fluid (known as endolymph)along the horizontal semicircular canal,generated by the induced thermalgradient, which leads in turn to athermo-convective force. This wouldproduce a displacement of the endolymph,thereby stimulating the canal’s sensorycells, in the same way as an angularmovement of the head (Fig. 2.1.6.8). Atthe turn of the last century, RobertBàràny, a Viennese specialist, receivedthe Nobel Prize for proposing thismechanism of caloric stimulation.

The microgravity of spaceflight, where normal thermal convection is absent, is idealfor verifying this mechanism. If the thermo-convective hypothesis is correct, then nonystagmus response should be observed. Caloric irrigation was first performed duringthe Spacelab-1 flight, and then on subsequent missions. In all test subjects, the caloricnystagmus response was elicited. A number of possible alternative sourcemechanisms for the latter have since been discussed. They include a direct thermal effecton the sensory hair cells or the afferent nerve connections to the CNS, or differentialpressure effects due to thermal expansion of the endolymph fluid in the labyrinth.

- How does the Brain Differentiate between Linear Acceleration and Gravity?

Space research has significantly improved our understanding of the working of the


that form synapses with vestibular hair cells, and vestibular nuclei neurons – and themotor neurons. The latter receive inputs from axons of the vestibular nuclei neurons,composing the vestibular reflex pathways. The vestibular system also receives inputsfrom the proprioceptive system, which is involved in the control of muscle length andtension, and from the visual system, which is involved in the control of eyemovements. Little is known about the exact nature of these interactions and virtuallynothing concerning the development of these connections.

Morphological data, concerning potential changes in the vestibular end organsresulting from exposure to weightlessness, are scarce so far, but they indicate thatsignificant changes may occur. In the rat, about a twofold increase in ribbon synapsesof Type-II hair cells and a 50% increase in Type-I cell synapses of the otoliths have beenfound after two weeks of space flight, compared with ground-based controls(Fig. 2.1.6.7). The increased synapticlevels were still apparent in animalsassayed 14 days post-flight. In contrast,animals exposed to increased gravitylevels, through centrifugation, exhibitdecreased synaptic density levels. Thefunctional significance of these synapticchanges has not been determined. Dataon whether there are alterations in theotolith crystals are less clear, with somestudies suggesting that there arechanges, and others not. Few data areavailable concerning the physiologicalactivity of vestibular afferents inweightless conditions.

The impact on an animal’s behaviour of alterations in the development of its gravityreceptor systems, at the cellular level, is virtually unknown. The whole is more thanthe sum of the parts, and knowing only how cells perform in culture in space mayreveal little about how whole organisms will respond in weightless conditions. OnEarth, specific behavioural adaptations to gravity, such as the righting reflex, are seenin many species in various situations. Observations of behaviour in the absence ofgravity and the analysis of adaptive responses to exotic gravitational regimes canprovide valuable insight into the evolution, function, and regulation of the behaviourof organisms. For example, experiments on Earth indicate that gravity plays asignificant role in learning basic motor skills like swimming and walking. Will animals,launched into space at the point where they have never walked on Earth, always bebetter adapted to weightlessness than to Earth, or will the changes be transient? Willthey present a righting reflex in response to being tilted after they have been returnedto Earth, or does a critical period exist for developing gravity-oriented reflexes?

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Figure 2.1.6.7. Reconstruction in 3-D fromthe right utricular macula of a rat, flownon the SLS-2 mission (courtesy of M.D.Ross & D.L. Tomko)

Figure 2.1.6.8 The mechanism of caloricstimulation of the horizontal semicircularcanal (from ‘Clinical Neurology of theVestibular System’, Baloh and Honrubia(Eds.), F.A. Davis, Philadelphia, 1990)

during 1g inter-aural centrifugation,despite the absence of sensed gravity.After a period of adaptation, the internalestimate goes to zero and the astronautsperceive a full body tilt to the side. Thisfinding could only come from studies inweightless conditions, where there is no confounding influence of thegravitational acceleration. Anotherfundamental finding of this experimentwas that astronauts always felt tilted,never translated, during constant-velocity centrifuging in space flight.Therefore, despite the fact that theotoliths in weightlessness are stimulatedby head translation, and not by head tilt,the brain continues to interpret low-frequency linear acceleration applied tothe otoliths as being due to head tilt.

Using a simple ball-catching experimentin weightlessness, it has been shownthat this internal estimate of gravity is also used in movement planning andexecution. During the act of catching a ball on Earth, the brain estimates the trajectoryof the ball, accurately taking into account its downward acceleration due to gravity. Inspace, a seated astronaut had to catch a ball travelling at a constant velocity, incontrast to the constant acceleration that would occur on Earth. In the first trials, theastronaut failed to catch the ball in weightlessness, but later trials were moresuccessful. These results indicate that the compensation for gravitational accelerationis pre-programmed, based on a lifetime of experience in a 1g environment. However,this internal model of gravity adapts over time, presumably through the estimation ofthe object’s trajectory based on visual information.

- The Role of Neural Space Maps in Spatial Orientation

Vertebrate brains form and maintain multiple neural maps of the spatial environmentthat provide distinctive, topographical representations of different sensory and motorsystems. For example, visual space is mapped onto the retina in a two-dimensionalcoordinate plan. This plan is then remapped to several locations in the central nervoussystem. Likewise, there is a map relating the localisation of sounds in space and onethat corresponds to oculomotor activity. An analogous multi-sensory space map hasbeen demonstrated in the mammalian hippocampus, which has the importantfunction of providing short-term memory for an animal’s location in a specific


otolith organs, which act as linear accelerometers. Yet Einstein’s equivalence principlerequires that a linear accelerometer cannot discriminate between linear accelerationand gravity. On Earth, the otoliths are continuously exposed to gravity. Is thisinformation always coded in the otoliths’ afferent nerve activity to the brain?

During the Neurolab space mission in 1998, it was shown by the author that the eyemovement reflex evoked by constant linear acceleration along the inter-aural axis, so-called ‘eye counter-roll’, has the same amplitude in weightlessness as on Earth. OnEarth, the eyes counter-roll during a head tilt to the side in order to keep the retinaaligned with the vertical axis. Therefore,although on Earth the otolith organs arestimulated by both the shearing force inthe plane of the horizontal otolith organs(the utricle) and by gravity, it is only theshearing force that is at the origin of theeye counter-roll. In space, linearacceleration was generated by a short-arm centrifuge (Fig. 2.1.6.9). When thecentripetal linear acceleration deliveredby the centrifuge was 0.5g, the ocularcounter-rolling amplitude was about halfof that measured at 1g. This suggeststhat both the direction and magnitude ofthe linear acceleration with regard to thehead are taken into account by the brain.This result could not have been obtainedon the Earth’s surface in a 1g environment.

Because sensory systems often provideambiguous information, neural processes exist to resolve these ambiguities. A neuralmodel has been proposed recently, based upon physical principles, which may beused by the brain to help estimate linear acceleration and gravity. The hypothesis thatthe central nervous system can develop an internal estimate of gravity and of thebody’s vertical has been validated by the subjective perception of astronauts duringcentrifuging in space. At the beginning of the flight, during a 1g inter-aural accelerationin darkness, the astronauts perceived a 45° tilt to the side, very much like on Earth.However, as the mission progressed, they felt more and more tilted, until perceiving a90° tilt to the side on flight day 16. This simple result indicates that an internalestimate of gravity (the so-called ‘body vertical vector’) is used for the perception of theupright.

The internal estimate normally used on Earth (1g) carries over to the early period ofexposure to weightlessness. Therefore the astronauts continue to perceive a 45° tilt

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Figure 2.1.6.9. The ESA Visual-VestibularIntegration System, or off-axis rotator,used on the Neurolab STS-90 mission. In space, this short-arm centrifugestimulated the vestibular system through a0.5g or 1g linear acceleration directedalong the subject’s inter-aural axis,without the confounding effect ofgravitational acceleration

Figure 2.1.6.10. The ‘Ball CatchingExperiment’ conducted during theNeurolab STS-90 mission. In microgravity,a thrown ball will travel at an almostconstant velocity. The trajectory of thesubject’s arm and the activity of hisforearm muscles are recorded as he triesto catch it

the nervous system for more cognitive processes. In recent years, severalinvestigations carried out in space using virtual reality have revealed that highercortical functions, such as mental rotation of three-dimensional objects, therecognition of inverted faces, the detection of bilateral symmetry and depth, ormemorised navigation, are impaired in weightlessness. The combination of virtualreality with multi-EEG recordings (for the measurement of evoked-related potentialsand brain mapping) should soon provide exciting results on the adaptationmechanisms of cerebral functions in the absence of gravity.

- Three-dimensional Orientation of Eye Movements

On the Earth’s surface, two major sources of linear acceleration are normallyencountered. One is related to the Earth’s gravity. The gravitational force pulls thebody towards the centre of the Earth, and the body opposes this force to maintain anupright standing posture. The other source of linear acceleration arises in the side-to-side, up-down, or front-back translations of the head, which commonly occur duringwalking or running, and from the centrifugal force sensed when turning or goingaround corners. The body responds by tending to align the longitudinal body axis withthe resultant linear acceleration vector. Put in simple terms, one has to exert anupward force to balance gravity when standing upright, and to tilt in the direction ofthe turn when in motion. Very recently, scientists have discovered that on Earth theeye movements also reflect an orientation to the resultant linear accelerations duringturning. During either passive rotation, as in a centrifuge, or while walking or runningaround a curved path, the axis of eye rotation tends to align with the resultant axis ofthe summed linear accelerations.

In space flight, the gravitational force is no longer perceived. Since there is nolocomotion in space, exposure to centrifugal forces is also reduced. However, the linearaccelerations due to side-to-side, up-down, and front-back motion (translation) persist.Measurements have been made, by the author, of the perceptual responses of thesubjects to centrifugal force and of the axis of eye rotation (Fig. 2.1.6.9). Both were inagreement, confirming that the central nervous system relies on the direction andamplitude of the summed linear accelerations for both perception and compensatoryeye movements.

2.1.6.5 Terrestrial Applications of Neuroscience Space Research

Much of the neuroscience research in space is focused on understanding themechanisms involved in the brain’s interpretation of the body’s orientation in three-dimensional space. With sufficient information in hand, researchers can developprocedures to protect space crew members from related disturbances, especiallywhen they return to Earth after long space voyages. However, the results of thisresearch are also applicable to patients with gait and postural disorders of


environment. This neural map is particularly focused on body position and makes useof proprioceptive as well as visual cues. It is used by the animal to return to an earlierlocation.

This system of maps must have appropriate information regarding the location of thehead in the gravitational field. So it follows that the vestibular system must play a keyrole in the organisation of these maps. Only recently has this been demonstrated byexperiments carried out in space. During an experiment performed aboard Neurolab,rats ran along a track called the Escher staircase, which guided them such that theyreturned to their starting position after having made only three 90° right turns. OnEarth, rats cannot run this track, but in weightlessness it provided a unique way tostudy the ‘place cells’ in the hippocampus that encode a cognitive map of theenvironment. The rats had multi-electroderecording arrays implanted next to theirhippocampal ‘place cells’. The recordingsmade in space indicated that the rats didnot recognise that they were back wherethey started after only three 90° rightturns.

Such studies could help to explain thevisual illusions experienced by someastronauts when they arrive in space,such as the impression that the world isupside-down, and how the nervoussystem adapts to weightlessness asthese illusions disappear later in themission. They could also reveal howinformation on gravity is processed by

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Figure 2.1.6.11. These circles show the firing patterns of twentysimultaneously recorded ‘place’cells in the rat hippocampus. Eachcircle depicts the firing of a singleneuron, as the rat traverses a roundplatform. The areas in red representthe ‘place’, or location, on theplatform where that cell fired at ahigher rate; the areas in blueindicate locations where the cell didnot fire at all. The ensemble of theactivities of all of the cells in thehippocampus encodes a ‘cognitive’map of the rat’s environment, whichit uses to navigate through its world

Figure 2.1.6.12. A crew member on theNeurolab STS-90 mission wearing theVirtual Environment Generator (VEG) head-mounted display. This display generatedscenes that tested how the crew membermaintained orientation in space

available (see Section 3.2). A majorlimitation of these systems is that theyare unable to measure ocular torsion,which is essential for the comprehensivethree-dimensional measurement of eyemovement. Furthermore, the use ofconventional video limits the samplingrate to 50 or 60 Hz. The video-oculography technique developed for theGerman and European Mir missions, andlater for the Neurolab mission, providesadequate measurement of all threecomponents of eye movement (horizontal,vertical and torsional). A new generationof eye-tracking equipment currentlybeing developed for the InternationalSpace Station is based on so-called‘smart vision sensors’. Digital processingand storage will permit online imagesampling rates of up to 400 Hz, enablingthe correct measurement of rapid eyemovements, such as fast phases orsaccades. This development is also being tested and reviewed by an internationalgroup of neurologists and engineers, for application in both the space and the clinicalenvironments.

Clinically speaking, the study of vertical and torsional eye movements has also beenhindered by the lack of a reliable stimulation method. Eye movements induced byvoluntary pitch or roll head rotation (active or passive) have been the subject ofintensive investigation during space flight. The head movements were measured withangular rate sensors (Fig. 2.1.6.5). Such tests are now commonly used in clinics. Notonly do they allow testing with more natural movements on the part of the patient,but also they do not restrict the plane of testing to yaw. Dysfunction in vertical reflexeye movements in response to head pitch or roll has thus been observed in patientswith lesions of the brain stem and cerebellum.

The use of off-vertical rotation, performed by seating the subject in a conventionalrotational chair and then tilting the entire apparatus, has proved to be a reliable testof the otolith organs on Earth. This stimulation has been (and is still being) used onastronauts after space flight. It is also used in the clinic to detect vestibular lesions,which mainly affect the otoliths. Similarly, the short-arm centrifuge studies onastronauts in space, as described above, suggest that centrifuging might provide auseful test of otolith function on Earth. When the test subject estimates the subjective


neurological origin, including elderly people for whom falls may have especiallyserious consequences.

A relatively large number of individuals on Earth suffer from prolonged, frequently life-long, clinical balance disorders. Disorders like Ménière’s disease and traumatic injuriesof the inner ear can severely influence the quality of life. Currently, human space flightis the only means available for studying the human response to sustained loss andrecovery of inner-ear information.

Changes in the human body during space flight often resemble the effects of aging. In-flight observations of young astronauts have revealed similar degradation in balancecontrol to that which occurs with age in Earth-bound subjects. For example, decreasesin visual (near accommodation, distance perception, smooth pursuit) and vestibular(low-frequency vestibulo-ocular reflex, postural stability) performances are noted bothin astronauts in space and in elderly people on Earth. Problems associated with spatialorientation (subjective vertical) and navigation (memorising a path) are also commonto both groups.

In fact, the majority of people over 70 years of age report problems of dizziness andimbalance. Balance-related falls account for more than half of all accidental deaths inthe elderly. There is little understanding of why older people are so prone to falling.One possible cause could be the misalignment of the body axis to the summed linearaccelerations that are encountered during turning, while walking or running.Microgravity provides a powerful tool with which to discriminate between theresponse to the linear acceleration of translation and centrifugal force, and the linearacceleration of gravity. This cannot be done on Earth, where the body cannot separatecentrifugal and gravitational forces. Astronauts can experience this in space, duringrotation on a centrifuge, for example. The experiment described above, flown onNeurolab in 1998, has provided basic information about how alignment of the bodyaxis to the summed linear acceleration occurs. Specific parts of the cerebellum (thenodulus and uvula) control this type of spatial orientation and these studies shouldhelp in understanding the nature of the processing in these parts of the cerebellum.

The stimulation and measuring devices developed for space experiments are oftenvery sophisticated. Some of these techniques have subsequently found wide usage forpatients with vestibular disorders on Earth, and have become the standard in clinicalpractice. For example, the first equipment for recording eye movement using videocameras was developed by ESA in the early 1980s for the Spacelab missions (Fig.2.1.6.13). The most readily available system for recording eye movements in the clinicwas to measure the magnitude of the voltage surrounding the orbit with surfaceelectrodes. This method (known as electro-oculography) proved too inaccurate forscientific research, especially for recording vertical eye movements. More recently, anumber of two-dimensional, video-based pupil trackers have become commercially

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Figure 2.1.6.13. The first eye-movementrecording system, with a video camera,developed by ESA for experiments duringthe first Spacelab mission

of the Space Shuttle to Earth. This periodof return to the Earth’s gravity is veryinteresting for seeking new insights intothe nervous system’s capacity to re-adapt, which is somewhat equivalent tohealing after an injury. This portablesystem, known as ‘Pocket’, is battery-powered, because the Shuttle’s maingenerators are shut down during re-entry(Fig. 2.1.6.15). It has been used on 21Shuttle missions and allowed testing on41 astronauts between 1991 and 1996,making it the most ‘space-flown’ life-sciences equipment to date. Nowadays,this equipment is used in clinics asbedside equipment to test the recovery of these functions in patients after inner-earsurgery.

Similar clinical applications are already foreseen for the virtual-reality systemscurrently being developed by space agencies for the Space Station (Fig. 2.1.6.12). Also,in preparing for a manned mission to Mars, for example, it will be vital to haveappropriate spatial-motor training before performing extra-vehicular activities (EVAs)or tele-operational tasks. Virtual-reality training may be a way to train astronauts (aswell as patients on Earth) to compensate for their altered neurosensory responses.However, the use of virtual environments in space could potentially exacerbatemotion sickness, and therefore further studies in this area are needed.

As mentioned above, neural coding of spatial navigation may be affected by thechange from a 1g to another force background, and this may be related to some of theorientation illusions experienced by astronauts. The influence of altered gravityconditions (whether 0g as in space, or 0.38g as on Mars) on orientation andgeographical localisation should therefore be further explored, in both human andanimal experiments. There is also a critical need to evaluate the influence of long-termexposure to weightless conditions on the coordination of body activities andlocomotion, involving coordination of eye, head, torso, arm, and leg activities, and oncortical maps. Ground- and space-based centrifuges, body-loading conditions, andvirtual-reality conditions should be utilised for testing. Ultimately, limited exposure to


vertical during constant-velocity centrifuging,the amplitude of perceived tilt gives a goodindication of how the brain measures theresultant of linear accelerations. Suchestimation during centrifuging is morereliable than during a static tilt relative togravity because, again, it allows testing undermore natural conditions of motion.

In many cases, the results obtained in spaceprovide researchers with unique insights thatcan be applied in the search for treatments fordiseases on Earth. For example spacesickness, which is experienced by over half ofall astronauts during the first 72 hours ofspace flight, is a form of motion sickness. The symptoms and the signs (stomachdiscomfort, nausea, pallor, cold sweating andvomiting) are similar. Reports of ‘mal dedébarquement’, the renewed symptoms ofmotion sickness after returning from spaceflight, tend to strengthen the analogybetween space and terrestrial motionsickness. The symptoms occur in about 90%of astronauts returning from missions lastingseveral months. Although the physiologicalmechanisms underlying motion sickness are poorly understood, somecountermeasures used to limit the symptoms in astronauts have proved successful forterrestrial motion sickness. It has long been known that anti-motion sicknessmedications are less effective if given after the symptoms of motion sickness havealready appeared. The transdermal patch has been tested successfully for the firsttime on astronauts during space flight, to deliver a small dose of an anti-motionsickness drug (0.5 mg of scopolamine) over a period of 72 hours. The sametransdermal patch is now commonly used on Earth to deliver a different drug for thoseattempting to give up smoking. Air- and sea-sickness de-sensitisation programmes forpilots and sailors, which include repetitive exposure to rotating head and bodymotions, are also based on the vestibular training techniques used by astronauts priorto space flight. This training is based on the notion that the inner ear is more importantthan the eye in providing cues as to the orientation of the aircraft or ship.

A portable acquisition unit for the recording of eye movements and muscle activity,coupled with a visual stimulus generator, has been developed by CNES. It is designedto study the astronauts’ oculomotor and postural responses during the return phase

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Figure 2.1.6.14. The Video-Oculog-raphy (VOG) Unit, developed by DLRfor use on the ISS

Figure 2.1.6.15. A free-floating crewmember on the STS-78 mission, wearing ahead-mounted visual stimulator and avest carrying the ‘Pocket’ multi-channelportable recording system for measuringeye movement and muscle activity

artificial gravity during the course of an interplanetary mission might prove to be asufficient countermeasure for most of the detrimental effects of being weightless forlong periods. The image of returning cosmonauts being lifted out of their Soyuzcapsules in the steppes of Central Asia, placed in litters, and then whisked byhelicopter to the nearest hospital, as anxious medical personnel watch over them, willthen no longer deter the enthusiasts from wanting to fly to Mars.

Further Reading

Clarke A. 1998, Vestibulo-oculomotor research and measurement technology for theSpace Station era, Brain Research Rev., 28, p.173.

Clément G. 1998, Alteration of eye movements and motion perception in microgravity,Brain Research Rev., 28, p.161.

Clément G. & Reschke M.F. 1996, Neurosensory and sensory-motor functions. In:Biological and Medical Research in Space (Eds. D. Moore, P. Bie & H. Oser), SpringerVerlag, Heidelberg, Chapter 4, p. 178.

Gottleib G. 1976, The Neural and Behaviour Specificity, Academic Press, New York.

Groopman J. 2000, Medicine on Mars, The New Yorker, April 2000, p. 36.

Merfeld D.M., Zupan L. & Peterka R.J. 1999, Humans use internal models to estimategravity and linear acceleration, Nature, 398, p. 615.

McIntyre J., Berthoz A.. & Lacquaniti F. 1998, Reference frames and internal models forvisuo-manual coordination: What we can learn from microgravity experiments, BrainResearch Rev., 28, p. 143.

Morris R.G.M., Garrud P., Rawlings J & O’Keefe J. 1982, Placed navigation impairmentin rats with hippocampus lesions, Nature, 297, p. 681.

Reschke M.F., Bloomberg J.J., Harm D.L., Paloski W.H., Layne C. & McDonald V. 1998,Posture, locomotion, spatial orientation and motion sickness as a function of spaceflight, Brain Research Rev., 28, p.102.

Ross M.D. & Tomko D.L. 1998, Effect of gravity on vestibular neural development, BrainResearch Rev., 28, p. 44.

Wassersug R.J. 1999, Life without gravity, Nature, 401, p. 758.

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2.2 SPACE BIOLOGY

2.2.1 Cell and Molecular Biology

R. Bouillon, J. Hatton & G. Carmeliet


Several physiological systems are altered by spaceflight as a result of the exposure topsychological and physical stress, to cosmic radiation or to microgravity. Anunderstanding of the mechanisms by which these factors alter human physiology isobviously important for the prevention and treatment of spaceflight-relatedsymptoms.

One of the most intriguing questions related to the influence of exposure tomicrogravity conditions is: 'What is the nature of the 'sensor' for microgravity: Is it thewhole body, or is it at the tissue or cellular level, or even a sub-cellular structure?'Connected to this is the fundamental question of whether individual cells can sensechanges in gravity.

There are some specialist gravity-sensing (gravimetric) cells, but they are involved innormal plant growth and development, as discussed in Section 2.2.2. The discussionhere, however, concerns normal mammalian cells. Studies of different mammalian celltypes, cultured under simulated microgravity conditions or during spaceflight, showthat gravity may have an effect on isolated cells and that some of these effects are cell-specific and even function-specific.

The observed alterations, common to diverse cell types, include changes in cellproliferation and differentiation. The recent observation that the expression(transcription) of over 1600 genes in a human renal cell culture was altered inmicrogravity provides further evidence for a differential gravity effect on cell function.Although the mechanisms involved remain a mystery, the data suggest a role for thefilamentary network of the cell (cytoskeleton) and for the signal transductionpathways in these processes.


or signalling, network (Fig. 2.2.1.1). Through this process, the cells are told to deliverthe proteins, such as CD69, interleukin-1 and -2, and the interleukin-2 receptor, thatare necessary for an adequate immune response. In fact, the cells sense multiplesimultaneous inputs, resulting in the activation and integration of several signallingpathways. Microgravity is one of the stimuli that alters a normal growth response.

The observed inhibition of proliferation in microgravity cultures is most likely a resultof alterations in the cellular events that lead to the surface expression of the importantregulatory molecules, such as the interleukin-2 receptor. This process requiresinduction of gene transcription and of new protein synthesis within hours ofactivation.

In microgravity cultures, the surface expression of the interleukin-2 receptor is foundto decrease. However, the surface expression of those receptors that are pre-synthesized and stored in lymphocytes, such as CD69, can occur to a great extent inmicrogravity cultures and the expression level of interleukin-1 is actually enhancedunder microgravity conditions. This differential regulation indicates that microgravitymodifies cellular function in a complex manner. The changes seen in this cytokine


Spaceflight has been shown to produce consistent changes in the immune system andalso in the bones (see Section 2.1.5) of both humans and animals. For that reason, thefollowing discussion will focus mainly on the effect of microgravity on the cellsinvolved in the immune system and on the cells that are responsible for boneformation (osteoblasts).

2.2.1.2 Changes to the Immune System

The body’s defence against pathogens relies upon the coordinated action of differenttypes of leukocytes or white blood cells. Immunological studies performed post-flighton astronauts have consistently shown alterations in the numbers and activity ofcirculating white blood cells (leukocytes). In these studies, the circulating leukocyteswere found to be redistributed in a similar way to the redistribution produced by stresshormones. This alteration in monocyte abundance and leukopoiesis may contribute tothe retarded wound healing that has been observed in rats during spaceflight. In addition,a reduction in the activity of natural killer cells and T-lymphocytes has been observed.

The activation of T-lymphocytes plays an important role in various immunologicalresponses. Because of their critical role in the immune response, circulating T-cells aremaintained in a resting state of the cell cycle, their growth and differentiation beingstrictly regulated. Given the importance of this pathway in the immune system andthe decrease observed in astronauts, several groups have investigated this process,using cells cultured under microgravity conditions (Fig. 2.2.1.1). Comparable results tothe in-vivo data were obtained, but at present the underlying mechanism for theobserved changes remains only partially understood.

- Proliferation and Cell Death (Apoptosis)

Experiments in microgravity and in ground-based model systems have clearlyindicated that, in a reduced-gravity environment, human T-lymphocytes fail toproliferate in response to mitogenic lectins, which would normally stimulate suchproliferation. In addition, the death rate of these cells (apoptosis) is found to increasein microgravity. These data suggest that the reduced response of certain cell types togrowth stimulation during spaceflight is partially a result of increased apoptosis.

- Gene Expression

The entry of T-cells into the cell cycle (mitogenic stimulation) is accompanied by theactivation of numerous cellular events. These include gene transcription and theexpression of activation markers on the plasma membrane.

In a normal simple growth response, an external inducer is docked at the surface ofthe cell and the command is transduced into the cell via an internal communication,

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Figure 2.2.1.1. A model of microgravity-induced effects on T-lymphocytes. Microgravity hasno effect on ligand binding or cell – cell interaction, but interferes with signal transductionvia the protein kinase C (PKC) pathway and cytoskeleton. This results in altered geneexpressions of interleukin-1 (Il-1), interleukin-2 (Il-2) and interleukin-2 receptor (Il-2R). Otherintracellular processes function normally, as evidenced by the normal expression of CD69.These changes lead to decreased proliferation and an increased cell death rate (apoptosis)

signalling pathways inside the cell, certain functions of these cells are modified undermicrogravity conditions.

2.2.1.3 Changes to the Skeletal System

Bone is a multifunctional organ that has to fulfil two main roles. One is the provisionof mechanical integrity, for both locomotion and protection. The other is aninvolvement in the metabolic pathways (homeostasis) associated with mineralregulation and control (see Section 2.1.5).

Bone is a dynamic tissue and in healthy individuals the amount of bone produced bythe bone-forming cells (osteoblasts) is of the same magnitude as the amount of boneresorbed by the bone-resorbing cells (osteoclasts). The amount and the architecture ofbone are regulated by hormones and local growth factors, as well as by themechanical factors.

Mechanical factors are essential for the maintenance of skeletal integrity, thearchitecture of bone being correlated with the mechanical stresses exerted upon it,resulting in a material with an optimal functional design. The target cells that respondto the mechanical signal produced by skeletal loading have not been identified withcertainty. They probably include osteocytes, osteoblasts, bone lining cells, andpossibly marrow stromal osteoblast progenitors.

In the weightless conditions of spaceflight, the consequent skeletal unloading hasbeen observed, in both humans and rats, to induce a series of events in bone whichresults in bone loss and compromised bone mechanical properties. It has beenestimated that, in a microgravity environment, on average about 1 – 2% of theskeleton is lost each month. Bone mass changes are, however, site-specific, rather thanevenly distributed throughout the skeleton. The tendency is for weight-bearing bonesto be more affected by microgravity than non-weight-bearing bones. In addition, theflight’s duration and the level of bone remodelling before unloading also appear to befactors able to modulate bone response to microgravity. Although no pathologicalfractures have yet occurred, spaceflight-related bone loss may have potentially seriousconsequences in long-term spaceflight, especially as recovery is a lengthy process.

Recent biochemical data from astronauts has confirmed the previous findings in rats,namely that microgravity induces an uncoupling of bone remodelling betweenformation and resorption that could account for bone loss. All bone-formationparameters were decreased, whereas bone resorption markers were increased whenmeasured during flight. Analysis of bones from rats flown on space missions showsdecreased bone formation and defects in bone maturation, suggesting inappropriatefunctioning of the bone-forming cells (osteoblasts) themselves when in microgravity.Interestingly, these histological findings are preceded by a detectable reduction in


production process in microgravity do not involve a general shutdown. Rather,microgravity appears to modify only certain signalling pathways.

- Mechanisms

One of the most intriguing challenges of microgravity research in this area is tounderstand how an identical chemical input produces, under altered gravityconditions, a different functional output in T-lymphocytes or other cell types. In tryingto elucidate this issue, investigators have concentrated their research on cell–cellcontact and cell morphology on the one hand, and on the different steps in thesignalling cascade on the other.

Cell morphology and motilityMicrogravity-induced alterations in the cytoskeleton are thought to underlie some ofthe effects seen in these changes to proliferation and gene expression. Humanlymphoblastoied cells, cultured under microgravity conditions, have shown a time-related change in microtubule appearance, with diffuse, shortened microtubulesextending from poorly defined microtubule organizing centres.

Cell–cell interactions and aggregate formation are important means of cellcommunication and signal delivery in T-lymphocyte activation. Electron-microscopyobservations of lymphocyte activation have indicated that surface contact betweenmonocytes and lymphocytes does occur in microgravity culturing. As alreadymentioned, synthesis of interleukin-1 is normal under (simulated) microgravityconditions. This synthesis occurs in response to intercellular signalling between T- cellsand monocytes and it requires cell–cell contact. This suggests that intercellularsignalling can occur effectively under altered gravity.

Correlated with this process is the ability of lymphocytes to traverse the interstitium.Culturing human lymphocytes under microgravity conditions, however, impaired theircapacity to locomote. These data suggest that specific types of cell–cell andcell–matrix interactions, in which adhesive and cytoskeletal proteins are involved, arealtered by gravitational changes.

Signal transductionSeveral experiments have demonstrated that the binding of an extra-cellular stimulusto its receptor was normal under microgravity conditions. This suggests that it is theintra-cellular signalling network that is modified by a change in gravity. Surprisingly,microgravity does not disturb all of the different signalling pathways at once, butalters rather specific subsets of a certain signalling cascade (protein kinase C).

In summary, under altered gravity conditions certain types of white blood cells showa decreased response to growth stimuli. Due to alterations in specific subsets of

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was observed in flight cultures. In contrast, a decreased number of cells were detectedin a mouse osteoblastic cell line after spaceflight.

- Gene Expression

Gene expression for matrix proteins, growth factors and receptors are altered whenosteoblastic cells are cultured in microgravity. The production of matrix proteins is anessential feature in the differentiation of the osteoblast and is required formineralisation. Human osteosarcoma cells, MG63, showed a reduced gene expressionfor several osteoblast-related matrix proteins (collagen-I, alkaline phospatase andosteocalcin) when cultured in microgravity. These data are consistent with the in-vivofindings. However, in a human foetal steoblastic cell line, no changes were detected inthe expression of several of these proteins. The differences in cell type and in theculture settings are possible explanations for the (apparent) contradiction.

In bone, a clear interaction exists between the different cell types, and osteoblastsplay an important role therein by secreting and responding to several growth factors.Under microgravity conditions, the message level of interleukin-6 and insulin-likegrowth factor binding protein-3 is increased, whereas insulin-like growth factorbinding protein-5 and -4 mRNA levels are decreased. In addition, the mRNA level forplatelet-derived growth factor-ß receptor was reduced in microgravity culturescompared to ground controls, whereas the epidermal growth factor receptor wasunaltered.

- Possible Mechanisms

The mechanisms by which osteoblastic cells respond to gravitational stress are stilllargely unknown. Among several possibilities, nitric oxide and protein kinase-C mightact as early mediators of non-gravitational mechanical stimulations, but only a fewstudies have investigated signalling pathways in altered gravity conditions.

Cell MorphologyChanges in cell morphology have been observed after 4 days of microgravity exposurein rat osteosarcoma cells, resulting in a morphologically mixed cell population.Changes were also observed in mouse osteoblastic cells, which became rounded. Nomajor changes in cell focal adhesion parameters were detected in the former cells aftera short period of simulated microgravity (clinostat), whereas gravity variations(parabolic flight) induced a significant decrease in cell area that was associated withreorganization of the focal contact plaques. However, after longer exposures tomicrogravity, the focal adhesions of those cells were modified. The cytoskeleton of themouse osteoblastic cells that were flown had a reduced number of stress fibres andthe nuclei of these cells were smaller, oblong in shape, and with fewer punctate areas.In contrast to these findings, no qualitative differences were observed in the


gene expression of bone-related proteins. In addition, spaceflight alters the messagelevel for local growth factors.

Bone formation occurs by the bone forming cells or osteoblasts, which first proliferateand thereafter start to secrete bone-matrix proteins. In this way, a typical bone matrixis produced that becomes mineralized. These processes can be studied in-vitro usingosteoblastic cell cultures. A decreased osteoblast function is claimed to play a role inthe process of spaceflight-induced bone loss. The underlying mechanism may involvean altered cellular behaviour when osteoblasts are exposed to microgravity. Recentexperiments, using several osteoblastic cell types (Table 2.2.1.1) show that cellmorphology, as well as the gene expression of growth factors and matrix proteins, isaltered under microgravity conditions.

Most of the studies listed in Table 2.2.1.1 used ground-based samples as a comparisoncontrol to the space experiments. Ideally, of course, an in-flight 1g centrifuge shouldbe used to provide for controls, in order to ensure an equivalent environment.

- Proliferation

Several different osteoblastic cells, derived from different species, have been studiedduring spaceflight. In both rat and human osteoblastic cells, normal cell proliferation

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Table 2.2.1.1. The effect of microgravity on osteoblast cells in-vitro

Cell Type Origin of Cells Micro-g Treatment Major Parameter Period Tested

ROS17/2.8 Rat osteosarcoma 6 days Cell morphology, cell line cytoskeleton

MC3T3-E1 Mouse 4 days Cell and nuclearosteoblastic cells morphology

Rat osteoblastic Femur marrow 5 days Gene expression:cells cultures cytokines

Rat osteoblastic Femur marrow 4-5 days Vitamin D Gene expression: cells cultures growthfactor receptors

MG 63 cells Human 9 days Vitamin D Gene expression:osteosarcoma cell line TGFβ matrix proteins

hFOB 1.19 Human foetal 17 days Cytodex beads Gene expression: osteosarcoma cell line growth factors,

matrix proteins

Many researchers have considered direct cellular gravi-sensing to be impossible, sinceat the mechanical level the force exerted by gravity on intracellular structures andbiochemical processes is significantly lower than the system’s thermal noise.Nevertheless, changes in cell function clearly do occur. So, if the indirect effects ofgravity can be excluded, this then provides an interesting and exciting problem.However, many potential artefacts have been identified in studying gravitationalbiology. The characterizing and quantifying of these potential artefacts needs to beincorporated into the planning and design of future experiments in this area, if gravi-sensing mechanisms are to be clearly identified.

Potential extra-cellular/indirect gravi-sensing mechanisms are: (i) effects related to the absence of buoyant convection flows in microgravity(ii) sedimentation (or lack of sedimentation) of non-adherent cells, resulting in altered

cell–substrate contact and cell–cell contact.

The first process could result in modified mixing of the culture medium, leading toalterations in gas exchange, to changes in autocrine or paracrine stimulation bysoluble growth factors, or to altered disposal of nutrients and waste products. Thesecond effect could be particularly important for leukocytes which, although notanchorage-dependent for growth, are certainly modulated by contact with cellsurfaces. Potential intracellular (direct) sensing mechanisms include gravi-sensing bysedimentation of intracellular structures.

2.2.1.6 Conclusion

The absence of gravity has major effects on the immune defence system (immunecells) and on the skeleton. Apart from possible indirect influences, via systemic stresshormones, isolated cells grown in culture during spaceflight also show abnormalitiesthat resemble the in-vivo effects observed in astronauts and animals.

Cell and molecular biology studies have tried to identify the precise mechanism bywhich isolated immune cells and bone cells sense microgravity, and what thesubsequent consequences are. The pathways involved have been partially identified.No generalized shutdown of cellular activity is observed. Rather, there is a decrease in specific proteins (interleukin-2 and interleukin-2 receptor), most likely due tointerference in the protein kinase-C pathway. Whether this pathway-specific alteration is related to the changes seen in cell morphology has not yet beenelucidated.

Also, the altered behaviour of osteoblastic cells under microgravity conditionscorrelates with the reduction in bone formation observed in humans and animals.Most of the osteoblastic cells that have been tested proliferate normally inmicrogravity, but their differentiation and response to stimuli are altered, as seen in


morphology or extracellular matrix of human foetal osteoblastic cells between theflight and ground-control cultures.

Signal TransductionOnly limited investigations of the different signal transduction pathways inosteoblastic cells under altered gravity conditions have been carried out so far. Thesesuggest that certain signalling pathways may be disturbed in microgravity.

In summary, in microgravity the proliferation of osteoblastic cells seems to proceednormally, but the production of bone matrix proteins is evidently hampered. A co-ordinated action between osteoblasts and osteoclasts is required. Growth factors,synthesized by osteoblasts, play an important role in this communication betweenbone cells. The production of several of these growth factors is altered whenosteoblastic cells are cultured in microgravity.

Studies investigating the underlying mechanism of this altered cell behaviour suggestthat the morphology of osteoblastic cells is changed and that the contact between theosteoblastic cell and the matrix is reduced. These two cellular aspects will influencethe level of gene expression.

2.2.1.4 Ground-Based Research

Because of the complexities of spaceflight, scientists have searched for ground modelsof simulated gravity. Recently it was demonstrated, using identical cell types andcomparable culture conditions, that a clear distinction exists between clinorotationand microgravity culture, depending on the cell type used and the processinvestigated. These data indicate that whereas clinostats are a very good modellingsystem for mimicking some of the effects of microgravity culture, they are only anapproximation. Experimental results must therefore be interpreted accordingly.However, in view of the complexity of spaceflight experiments and the fact that clino-rotation is the best available terrestrial model system for studying the effects ofreduced gravity on cells, clinostat studies continue to play an important role.

In addition, other aspects of spaceflight, such as the vibrational force and theincreased acceleration during launch, can alter gene expression in osteoblastic cellsand have to be taken into account when analyzing spaceflight data.

2.2.1.5 The Nature of the Gravisensor

The mechanism by which normal cells can sense changes in gravity remains amystery. Theoretically, gravity can potentially be sensed either indirectly, throughgravity-dependent changes in the extra-cellular environment, or directly, by sensinggravity-dependent changes within the cell.

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2.2.2 The Role of Gravity in Plant Development

G. Perbal


Land plants are a prime constituent of the animal and human food chain. They providenot only the carbohydrates, but also the proteins and lipids, the vitamins andantioxidants, which are a vital part of the human diet. They also sustain the oxygen ofthe atmosphere and assist in controlling the level of carbon dioxide, the dominant'greenhouse' gas. A detailed understanding of all aspects of their growth is thereforeof obvious importance to mankind.

When plants left their aquatic environment some 400 million years ago, to evolve andspread across the land masses, they encountered a gravitational force about athousand times larger than that to which they had been subjected in the buoyantconditions of their original underwater environment. Consequently, they have evolvedon land with gravity as a major determinant for their form and growth.

Gravity has been shown to play a major role in the orientation of plant organs(gravitropism) and in plant morphogenesis (gravimorphism). Gravitropism is abending response, due to a change in orientation or to an inadequate orientation of anorgan with respect to gravity. For example, when a root germinates, its tip can beinitially orientated at random in the gravitational field, but it must penetrate quicklyinto the soil to assure the survival of the seedling. If the root is placed horizontally, itsapex bends downwards (Fig. 2.2.2.1) and the curvature is almost completed after 2 h.This curvature is due to differential growth of the upper and lower sides of this organ.


the changed expression pattern of matrix proteins and growth factors. Elucidation ofthe signalling pathways involved has only recently been started.

These reported data suggest that gravity has an effect on certain cell types and itaffects a limited number of cellular functions and pathways. Exactly how isolated cellsthat are not specialist gravi-sensing types can sense a change to microgravityconditions is yet to be determined. The answers to such questions are not onlyrelevant to understanding the effects of microgravity on living organisms during futurespaceflights and to preventing specific problems in astronauts, they will also increaseour understanding of the fundamental processes in normal cell physiology, and maywell provide links to the patho-physiology of certain diseases, such as age-relatedbone loss or immune disorders.

Further Reading

Hammond T.G., Lewis F.C., Goodwin T.J., Linnehan R.M., Wolf D.A., Hire K.P., CampbellW.C., Benes E., O'Reilly K.C., Globus R.K. & Kaysen J.H. 1999, Gene expression in space,Nature Medicine, 5 p. 359.

Tailor G.R. 1993, Overview of spaceflight immunology studies, J. Leukoc. Biol., 54, pp. 179 – 188.

Marie P.J., Jones D., Vico L., Zallone A., Hinsenkamp M. & Cancedda R. 2000,Osteobiology, Strain, and Microgravity: Part I. Studies at the Cellular Level, Calcif.Tissue Int., 67, pp. 2 – 9.

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Figure 2.2.2.1. Gravitropic curvature of a lentil root as a function of time. The seedling washeld in place by a metal bar and grown in a vertical position for 27 hours. It was thenplaced horizontally (0 h) for 3 hours. The counter reaction, which occurred after 3 hours,is indicated by the arrow and led to a reduction in the angle of curvature. C = cotyledon,cr = counteraction, s = sponge, r = root

2.2.2.2 How Plants Orientate With Respect To Gravity

- Perception Site of Gravity

Since plants are static, the survival of young seedlings depends upon, among otherthings, their correct orientation. This is established by using the direction of the localgravity vector as a guide to their growth. That growth is based on a highly complicatedstimulus response chain, in which the gravity stimulus is first transformed into abiochemical signal. This signal is then transmitted via several cells, probably bycell–cell communication, to the relevant growing tissue. The scientific objectives ofspace experiments in this area tend to be focused on the details of the structure ofgravity-sensing cells, upon the way cell structures could act as gravity sensors and thesensitivity of those sensors.

At the beginning of the 20th century, it was discovered that a special tissue (called‘statenchyma’) in roots and in shoots contains movable organelles (statoliths) in theircells (statocytes), which sediment under the influence of gravity (Fig. 2.2.2.2). Theseorganelles possess large starch grains, which are denser than the surroundingcytoplasm. In animal cells, the statoliths lie outside the cell, whereas in plants they areinside.

Experiments involving the removal of the root cap, or ablation of the statocytes witha laser beam, have demonstrated that these cells are necessary for gravitropism inroots. In shoots, the role of the statocytes was confirmed recently by the analysis ofan agravitropic mutant of Arabidopsis thaliana, which lacks statenchyma. It has alsobeen shown that sensitivity to gravitropic stimulus is much greater in the root capthan in any other region of this organ. For this reason, it is generally accepted that thestatenchyma cells in roots and shoots are the site of gravity perception.

However, despite many observed correlations, the actual role of statoliths in theperception of gravity still remains to be conclusively demonstrated. Statolithssediment because of the density of starch. However, studies on starch-depletedmutants, as well as experiments leading to a lowering of the starch content, haveindicated that the movement of the statoliths is not an essential requirement.Consequently, these organelles cannot be the only structures that can perceive gravity.Some researchers have argued that the whole protoplast (i.e. the cell itself) could alsoplay this role.

This continuing controversy is due to the fact that the perception phase of the gravitystimulus, which takes place in the statocytes, is not easy to investigate on the ground,where it is impossible to remove gravity. Space therefore offers a unique opportunityto study the sensitivity to and perception of gravity.


The optimal direction of growth for the primary root is along the gravity vector andthis organ therefore shows positive gravitropism (Fig. 2.2.2.2). By contrast, the shoothas a negative gravitropism, since its apex is oriented in the opposite direction.Secondary roots and lateral branches grow obliquely with respect to gravity and theirgravitropism is positive or negative, respectively. Only a few organs do not show anypreferential direction of growth and are for this reason classed as agravitropic. Thusthe whole morphology of plants depends upon gravity.

Despite over a century of research into the mechanisms by which plants respond togravity, the details of several important aspects have remained uncertain. Only withthe opportunity to remove the gravitational force almost entirely, by experimentationin microgravity, has it finally been possible to begin to unravel the details ofgravitational response. In space, with the aid of a centrifuge, gravity can be a variableparameter ranging upwards in value from almost zero. Details of gravitationalsensitivity and the time scales for the various responses can now be explored in a waythat was hitherto impossible.

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Figure 2.2.2.2. Orientation of plant organs with respect to gravity and localisation of thegravi-sensing cells in the stem and roots. The gravitropic behaviour is indicated inparentheses. Inserts: localisation of the statenchyma in the shoot and in the root. S = statocytes; e = epidermis; p = parenchyma; QC = quiescent centre; RCM = root-capmeristem; PC = peripheral cells; g = gravity

to the microgravity sample. It has been suggested that this apparent discrepancy isdue to the fact that the 1g control in space was subjected to microgravity for 15 minutes, prior chemical fixation. Thus, within 15 minutes, the nucleus was able tomove (about 0.8 µm) from the proximal plasma membrane towards the cell centre. Itwas therefore proposed that the nucleus is attached to the cell periphery by actinfilaments, and that these filaments are sensitive to tensions created by the weight ofthis organelle. It has been suggested that the nucleus’ displacement was due to arelaxation of the cytoskeleton. However, this organelle remained attached to the actinfilaments, since a 1g centrifugation of the lentil seedlings grown in microgravitycaused a movement of the nucleus towards the proximal wall.

As noted above, the statoliths in microgravity are located in the proximal part of thestatocytes. The 1g control in space shows a different distribution of these organellescompared with the 1g control on Earth. The reason for this difference between the twocontrols has been elucidated. It was demonstrated using a sounding-rocket flight thatthe transition from 1g to microgravity for about 6 minutes was sufficient to provoke


Data on sensitivity are required in order to understand the mechanisms of sensing ingeneral, and this data can be obtained in space with the aid of a centrifuge. Thegravitational force imposed can thereby be varied upwards from essentially zero. Theresults from space experiments have demonstrated an astonishingly high level ofsensitivity of plant organs to gravitational stimulus. The minimum force that is sensedby plant organs is about 1/1000th of the Earth's gravitational field. The minimum'dose' is about 25 g sec. In other words, a 25 second exposure of plant roots (in ahorizontal position) to 1 g triggers the stimulus response chain for gravity-orientedgrowth.

These results indicate that the root is able to perceive its orientation with respect tothe gravity vector and to generate a signal of curvature in less than half a minute.

- The Structural Polarity of Gravity-Sensing Cells

The structural polarity of the statocytes has been studied intensively on the groundand can be considered to be relatively constant from one species to another. Thenucleus of gravity-sensing cells is always situated close to the proximal wall, whereasthe statoliths are sedimented on large aggregates of endoplasmic reticulum tubuleslocated along the distal wall (Fig. 2.2.2.3A).

One of the most intriguing observations made in microgravity concerns the positionof the nucleus within the statocyte. In microgravity, this organelle is closer to thelongitudinal axis of the statocyte, in a more central position than in the statocytesdifferentiated on the ground (Fig. 2.2.2.3B). Some observations have indicated thatthere is a denser region between the plasma membrane and the nucleus’ envelope.This suggests that the nucleus could be attached to the cell periphery by someelements of the cytoskeleton (actin filaments). This hypothesis was confirmed by atreatment that perturbed the polymerisation of the actin filaments and provokedsedimentation of the nucleus under the influence of gravity, providing a more centraldistribution of this organelle in microgravity.

Another unexpected result was obtained by studying the distribution of theamyloplasts in microgravity. These organelles should have been distributed randomlyin the absence of a gravitational field. However, in the lentil statocyte they werepreferentially located in the proximal part of the cell, around the nucleus. A three-dimensional reconstruction has shown that the amyloplasts were also not distributedat random in the statocyte of white clover grown in microgravity.

- Movement of the Nucleus and Statoliths in Microgravity

In microgravity, the location of the nucleus in the lentil root statocyte was differentfrom that observed in 1g on the ground. Yet in the 1g control in space it was very close

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Figure 2.2.2.3. Root statocytes of lentil seedlings grown for 28 hours.A. Flight control (F1g), in which the seedling was centrifuged at 1g in space.B. The seedling was grown in microgravity (Fµg).a = amyloplast; g = gravity; mi = mitochondria; N = nucleus; nu = nucleolus; dw = distal wall; pw = proximal wall; RE = endoplasmic reticulum

roots and cress roots. The fact that the amyloplasts are attached to actin filaments andare moved along these filaments by motor proteins led to the proposal of a completelydifferent mechanism for the transduction of the gravitropic stimulus. According to this,the amyloplasts could create tensions within the actin network on the ground. Astimulation could provoke a change in the tensions on the actin filaments (Fig. 2.2.2.4b) and activate mechano-sensitive ion channels.

Thus, research in microgravity has led to a new concept for the transduction of thegravitropic stimulus, which implies a role for the actin network in the transformationof the mechanical effect of gravity (statolith movement) into a biochemical factor(calcium efflux). Recently the role of actin has been questioned, since it has beenshown that treatment with cytochalasin D, which perturbs actin polymerisation, doesnot prevent gravitropic reaction. However, it has been proved that, after the transferfrom 1g to microgravity of lentil seedlings treated with cytochalasin D, there was stilla movement of the amyloplasts. This result indicates that a cytochalasin D treatmentactually perturbs the formation of the actin network, but does not prevent itcompletely.


movement of the amyloplasts toward the nucleus. The researchers pointed out thatthe gravitational force on the ground is greater than the basipetal force exerted by thecytoskeleton. However, in microgravity this basipetal force becomes prominent andthe amyloplasts are pulled towards the nucleus. Unfortunately, because of the shortduration of the flight, it was not possible to see if this movement would continueduring a longer period of microgravity. Recently, the kinetics of the movement of theamyloplasts have been studied: (i) in the gravitational field, by putting roots in theupward position, and (ii) by transferring lentil seedlings grown in a 1g centrifuge tomicrogravity.

The velocity of the displacement was seven times greater in the inverted roots on theground than in roots grown in 1g and transferred to microgravity. In roots treated bycytochalasin D, the movement observed in microgravity was much slower than thatobserved in non-treated roots. These results show that on the ground some forcesexerted by the cytoskeleton cannot be detected simply because their intensity isbelow that of the gravity force. The fact that the transfer from 1g to microgravityinduces some displacement of the cell organelles demonstrates that the cytoskeletonis able to react to tension existing within its filament networks.

- Transduction of the Stimulus

The nature of the gravity sensors is not yet known and it is difficult to determine whichcellular structure contains the receptors. These receptors are able to transform themechanical effect (the potential energy dissipated) into a biochemical factor (e.g.calcium efflux). It has been suggested that the endoplasmic reticulum, which is mainlysituated at the basal pole of the statocyte (Fig. 2.2.2.4a), could be involved in thetransduction step of gravistimulation. Due to the geometry of the statocyte, anasymmetrical message could be created in the root cap. This hypothesis is consistentwith the fact that it is well established that the concentration of cytosolic calcium isvery low, whereas its concentration in the endoplasmic reticulum is much greater. Itwas therefore proposed later that the result of the amyloplast exerting a mechanicalaction on the endoplasmic reticulum could be to provoke an efflux of calcium and tolocally increase the calcium concentration. This could activate some Ca2+ -dependentproteins as calmodulin. This protein could in turn activate (eventually after a cascadeof events) an auxin pump and a Ca2+ channel.

In fact, the results obtained from microgravity experiments are not in agreement withthis hypothesis. In microgravity, the amyloplasts of the root-cap cells are located closeto the proximal wall, i.e. far from the distal endoplasmic reticulum (ER) membranes. Incontrast, in the 1g centrifuge these organelles are sedimented onto these membranes.If the original hypothesis was correct, roots grown in microgravity should be muchless responsive than those grown in 1g, since only a few contacts between ER andstatoliths were possible. However, the opposite result was obtained, for both lentil

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Figure 2.2.2.4. Cytoskeleton and statocyte polarity. (a) statocyte of a root placed vertically;(b) statocyte of a root stimulated in the horizontal position. The amyloplasts (A) and thenucleus (N) are in contact with actin filaments (MF), which are attached to stretch-activatedion channels (asterisks). These channels are open or closed, depending upon the tensionexerted by the actin filaments. In stimulated statocytes (b), the tension in the actin networkincreases in the upper half of the cells and decreases in the lower half. This leads to anasymmetrical efflux or influx of ions in the cell. ER = endoplasmic reticulum; black dots =microtubules (from A. Sievers and M. Braun, in 'Plant Roots', Dekker, New York, 1996)

2.2.2.3 The Role of Gravity in Plant Development

The scientific interest in the influence of gravity on plant development embracesgermination, cell division and elongation, the development of storage and supportingtissues, formation of flowers and propagating cells, pollination and the production offruit and seeds. The gravimorphism is the result of the developmental responses of theplant to gravity, i.e. the effects of this physical factor when the organs are orientedcorrectly with respect to the gravity vector. In principle, the action of gravity on plantdevelopment could easily be analysed by comparing plants grown in microgravityand plants grown on the ground. Unfortunately, the culture conditions in a spacecraftare completely different from those on the ground, because for example of thepresence of cosmic rays and the cabin atmosphere. For this reason, a 1g controlexperiment must be carried out in space in parallel, thereby subjecting the sample tothe same space factors as the microgravity sample. However, very few experimentshave so far been performed with such a space control.

On the ground, it is possible to simulate the action of microgravity (with a device calleda ‘clinostat’) by rotating the plant about a horizontal axis. The unilateral effect ofgravity is thereby compensated, but it is obviously still present. Analysis of plantdevelopment in microgravity and in the clinostat has shown that the latter cannotprovide a true simulation of microgravity.

- Germination and Root Orientation

Many species have been grown in microgravity and it appears that the absence ofgravity has no real effect on germination. However, the growth orientation of the rootof the embryo seed plant (radicle), which is strongly dependent upon gravity on Earth,is related to the position of the embryo in microgravity and the root tip can oscillatestrongly during germination. Such movements have been observed in lentil roots.After a growth period of 25 h in microgravity, the emerging root was bent and its tipwas in most cases pointing away from the cotyledons. Although the mean angle ofcurvature was about the same after 25 and 29 h, some roots were subject to a strongchange in orientation during these 4 h.

Root growth in cress was studied to determine whether the root tip was subject to arandom direction of growth (random walk) in microgravity. The seedlings were grownbetween two agar slices and the deviation angle of the root tip was measured withrespect to its initial orientation. The mean angle of deviation was about 0°, and thesquare of this angle of deviation increased proportionally with time, whichrepresented two characteristics of random walk. However, this random walk waslimited in duration.


- Gravitropic Curvature in Space

The involvement of the hormone auxin in gravitropism is well-established. TheCholodny-Went theory states that the lateral (downward) transport of auxin is thecause of the gravitropic bending. It operates by inducing a greater elongation of thelower side of the shoot (or coleoptile) and an inhibition of growth of the lower side inthe root. However, this hypothesis does not completely account for the patterns ofgravitropic bending.

For instance, the gravitropic response of lentil seedling roots was analysed during thefifth Shuttle to Mir mission. The lentil seedlings were grown in microgravity for 25 h andthen placed on a 1g centrifuge for 22 min. The gravitropic response was followed bytime-lapse photography for 3 h after centrifuging. In microgravity, the tip of thestimulated roots overshot the direction of the acceleration that was responsible for thegravitropic stimulus (i.e. the roots could bend by more than 90°), whereas the rootscontinuously stimulated on the ground did not reach the direction of the accelerationor gravity. Thus, in the Earth’s gravitational field, there must be gravity-dependentregulation (inhibition of root curvature). This regulation is observed when in some rootsthere is a kind of counter-reaction, which reduces the bending (cf. Figs. 2.2.2.1 and 2.2.2.5).

Thus, space experiments were very useful for the analysis of gravitropism, since theyhave provided new data on the perception and transduction of the gravitropicstimulus by the statocytes. These have shown that these phases could take place veryquickly, within less than half a minute. These experiments have also shown that thecytoskeleton is involved in the transduction of the gravitropic stimulus; in particularthe actin network should sense tensions exerted by the weight of the amyloplasts. Ithas been shown that the extent of the induced curvature is regulated by gravity on theground, in order to prevent overshooting of the vertical direction by the root tip.

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Figure 2.2.2.5. Curvature of lentil roots grown in microgravity, stimulated for 22 min andplaced back in microgravity for 3h. The roots overshoot the direction of the acceleration (a, arrow) that was responsible for the gravitropic response (from Perbal et al. 1999, ESA SP-1222, p. 251)

majority of these cells should be at the beginning of the second cell cycle. From thedata in Table 2.2.2.1 it can be concluded that, in 1g on the ground, more cells werefurther along in the process of the second cell cycle (more cells in the S-phase). Thismeans that the first cell cycle was faster on the ground, and also on the 1g centrifugein space, than in microgravity.

- Development of the Plant Body in Microgravity

Figure 2.2.2.6 summarises the changes occurring in microgravity in the developmentof plant organs. The orientation of the primary axis, which is vertical on the ground, isvariable in microgravity and to some extent the primary roots could be subjected torandom walk. The apical dominance of the primary root over the secondary roots isreduced in microgravity such that the latter elongate faster and are initiated very closeto the primary root tip.

A careful analysis of the results obtained on shoot development in microgravity hasindicated that, in general, growth was often reduced when the plants were subjectedto acceleration or gravity during the Shuttle’s launch and re-entry into the Earth'satmosphere. When the plants were grown in microgravity, growth was greater than in 1g.

The results obtained for lettuce on Salyut-7 were the most impressive and reliable,because there was a 1g control both in space and on the ground. Taking the length of


- Growth of the Primary Root

It has often been assumed that the effect of gravity on the primary root should beconstant, but it has been pointed out that it depends upon the stage of development.This was concluded after a careful analysis of the literature, which showed that rootlength was generally the same in microgravity and on the ground for a growth periodof less than 1 or 2 days, whereas it was greater in microgravity than in 1g for a growthperiod of 3 to 5 days. For longer periods of growth, the root length was smaller inmicrogravity than in 1g.

Plant hormones play a key role in the developmental processes of the root system,including control of the cell cycle in the apical meristem, elongation and lateral rootinitiation. As auxin and abscisic acid are considered to be involved in rootgravitropism, it was obvious that the role of these two hormones had to be analysedfirst, since their distribution in the plants grown in microgravity had more chance tobe perturbed. In a space experiment, the auxin and abscisic contents of maizeseedlings grown in microgravity were analysed. A significant difference was onlyobserved for auxin in roots.

- Cell Cycle and Mitotic Disturbances in the Primary Root Meristem

A study of mitotic activity and chromosome disturbances in the roots of three species(oats, mung beans and sunflowers) showed that cell division was substantiallyreduced in space. In oats and sunflowers, there were chromosomal aberrationsranging from an abnormal number of chromosomes, to breakage and bridgeformation. In mung beans, however, no chromosome aberration was detected.Evaluation of the available data indicates that indirect effects play a major role inthese modifications and that plants grown in space are subject to various stresses.

As noted earlier, the culture conditions in space are not always satisfactory, since thecabin atmosphere can contain gases (e.g. ethylene) that may affect plant growth. Thisproblem can be solved to some extent by using a 1g centrifuge in space. This can allowdiscrimination between the effects of microgravity and those due to other spacefactors (cosmic rays, cabin atmosphere).

For the majority of species investigated, a decrease in the mitotic index (MI = % of celldivision) was observed. It must be stressed, however, that MI is a very poor indicatorfor studying the cell cycle, because it can vary as a function of many different factors.For that reason, researchers have chosen rather to study the cell cycle and its variousphases (G1, S, G2, M) in a homogenous tissue (i.e. the cortical cells of the root). Theperiods of growth were 28 h and 29 h (see Table 2.2.2.1) for the Spacelab IML-1 (1992)and IML-2 (1994) missions, respectively. For the space-grown lentil seedlings of IML-1and IML-2, cortical cells have at most completed just one cell cycle. In principle, the

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Table 2.2.2.1. Percentages of the various phases (G1, S, G2, M) of the cell cycle in the primary rootmeristem of lentil seedlings, grown in space during the IML-1 and IML-2 Spacelab missions*

Cycle First Second

Phase G2 M G1 S

IML-1 G1g 11.2 7.2 55.4 26.228 h F1g 11.9 8.9 58.7 20.5G. Perbal & Fµg 27.9 6.8 55.5 9.8D. Driss-Ecole,Physiol. Plant,90, 313, (1994)

IML-2 G1g 10.6 4.0 52.8 32.629 h F1g 19.7 6.0 48.2 26.1F. Yu et al., Fµg 17.8 3.9 61.1 17.1Physiol. Plant,105,171, (1999)

* The percentages of the various phases were determined by image analysis, following Feulgen treatment. G1g = groundcontrol; F1g = flight control; Fµg = microgravity sample. IML-1 and IML-2 = International Microgravity Laboratory 1 (1992)and 2 (1994) missions.

that space factors other than microgravity could become prominent. That is why theresults of experiments without a 1g control are questionable.

Another problem is the fact that data must be numerous enough to be analysedeffectively statistically, which is in obvious contradiction with the need to use verysmall volumes or masses in space.

- Reproductive Development in Space

Several attempts to grow plants through a complete life cycle (from seed to seed) inspace have proved unsuccessful because of the delayed development and death of theplants. Arabidopsis thaliana has been the most successfully studied species in thisrespect, because of its small size and short life cycle. However, partial or total sterilityof the reproductive material that eventually did develop has also been observed in thisspecies.

Detailed study of the different types of hardware used in space has shown that before1997 about eight different types of hardware were used for plant-reproduction studies.Of these, those having some kind of ventilation permitted seed formation. Threedifferent experiments were performed on Arabidopsis with the Plant Growth Unit(PGU). The different degrees of success in subsequent reproductive development inmicrogravity were related to variations in the gas phase of the plant-growth chambers.In the first experiment, no viable pollen was observed and young megaspores weredeformed and empty. It was considered that during the experiment there was acarbohydrate-synthesis limitation due perhaps to a lack of carbon dioxide in theatmosphere. In a second experiment, the atmosphere was supplemented with CO2and the plant had mature pollen and normal embryo sacs. However, no fertilisationoccurred, because pollen was not released from the anthers. In a further experiment,air flow through the plant-growth chambers was provided and it was found thatdevelopment then proceeded normally in orbit, through to the stage of immatureseeds. The space-grown plants were similar to the ground control.

In these three experiments, the plants were launched after a period of 13 days ofcomplete vegetative growth on the ground. It is thus not possible to determine ifmicrogravity had an effect on their development before the reproductive stage.

Whether or not a seedling growing from the outset in microgravity can flower andproduce normal seeds remains a matter of debate. As the modifications observedduring the vegetative phase were quantitative rather than qualitative, one can arguethat it should be the same for the reproductive phase.

A series of recent space experiments should have provided an answer to this problem.Super-dwarf wheat was grown on board Mir. The height of the shoots was reduced by


the stem growing on the 1g centrifuge in space as 100%, a decrease in g-level led toan 8–16% increase in stem length.

It must be stressed that the growth of the shoot, as well as that of the root, in spacewas much slower than on the ground for this particular experiment. Doubtless otherspace factors were responsible for the slowing down of growth. In this respect, recentstudies have demonstrated the role of ethylene in the development of Arabidopsisthaliana grown in space. It was observed that flight seedlings (microgravity and 1gcontrol) were smaller (60% in total length) compared to the ground controls. Seedlingsgrown in space had two structural features that distinguished them from the control,namely greater root-hair density and an anomalous hypocotyl hook structure. It hasbeen shown that the slower growth and morphological changes observed in the flightseedlings may be due to ethylene present in the spacecraft, since plants treated with10 ppm of ethylene on the ground showed the same features as those in space.

Comparing the results for primary roots and shoots, it can be concluded that bothtypes of organs should have the same growth on the ground and in microgravityduring the first few days. Then there is an increased shoot and primary-root growth forless than one week. For longer periods, the growth of the primary root decreases, witha loss of apical dominance. Thus, microgravity could increase the biomass production,but only during the starting phase of the plant’s development.

It should be noted that in the space experiments the environment was mostly notcontrolled and that the atmosphere was not monitored in the growth chambers. Sincemicrogravity alone may have a slight but continuous effect on plant growth, it may be

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Figure 2.2.2.6. Summary of the effects of microgravity on the differentiation, developmentand direction of growth of plant organs

will continue to be necessary in order to develop the study of gravity sensing further.The ground experiments will be useful in determining the mechanisms for stimulustransmission and differential growth. In particular, the nature of the gravity sensorsmust be confirmed (statoliths versus protoplast) and the receptors must be identified(cytoskeleton). The role of Ca2+ and stretched ion channels must also be defined.

The analysis of plant development in space has shown that germination is normal inmicrogravity. However, even during the first phases of root growth, some differencescan be observed between plants grown in microgravity and in 1g. Although themorphology of the primary root is not strongly modified, there is a change in the rootcell cycle. The first cell cycle (after hydration) appears to be longer in microgravity thanin 1g, and after several cycles the delay seems to increase because the mitotic indexin roots grown in microgravity for several days is lower than in 1g. In microgravity, theapical dominance of the primary root over the secondary roots seems to be reduced.Thus, gravity is at least partly responsible for the apical dominance of the primary rootand seems also to be involved in the dominance of the apical meristem.

The reproductive phase is completed in microgravity when the culture conditions areadequate. A lot of problems encountered in growing plants in space are related to thefact that the physical environment is different in microgravity. There is the absence ofconvection, for example, and it is clear that the limitation of gas exchanges influencesplant growth.

A new generation of space experiments is certainly needed in order to confirm someof the most important results on the basis of improved statistics, by using moresamples and better plant environment controls than has been possible previously.Such experiments are expected to include the following objectives:– identification of possible gravity-related genes in general– determination of possible gravity-related genes in different organs– identification of possible ‘cross-talk’ between genes with different stimulus response

chains, e.g. gravity versus light– identification of proteins related to the gravi-stimulus response chain– determination of interactions of related proteins.

Future experiments will be performed using instruments such as EMCS, which will bebetter able to monitor and control the physical environment of plants in space. Inparticular, it will be possible to carry out experiments with a 1g control in space andwith a monitored gas composition of the atmosphere.

Growing plants and producing crops in space is a challenge that needs to be overcomefor the long-term future of space travel. The optimization of plant growth for thebenefit of agriculture on Earth, based upon a deeper understanding of plant growth,represents the major future ground-based return from these programmes.


half in microgravity and there were 2.7 times fewer headed shoots. No seeds werefound in the heads formed in space. The analysis showed that the most profoundchanges observed in the reproduction stage of this plant were caused by the toxiceffect of ethylene, rather than spaceflight factors. Its concentration in the Mir station’satmosphere was high enough to account for the modifications observed in space-grown wheat plants. These results show that the effect of microgravity should bestudied with facilities in which the atmosphere is perfectly controlled.

A recent analysis of the life cycle of Brassica rapa onboard Mir in the Svet greenhouseconfirms this hypothesis. It has been shown that gravity is not absolutely required forany step in the plant life cycle. However, seed quality is compromised by developmentin microgravity. In particular, seed size is reduced, and the reserves are stored in theform of starch rather than protein and lipid. It therefore appears that the reservesstorage too is perturbed in microgravity. It seems also that the utilisation of thesereserves is modified in the absence of gravity. The causes of these effects ofmicrogravity on metabolism remain to be determined.

2.2.2.4 Conclusion

Microgravity has proved to be a very useful tool for analysing the influence of gravityon plant orientation (gravitropism), since it is the only opportunity to remove gravityand hence to clearly measure such parameters as the sensitivity threshold.

The level of acceleration that can be perceived by the organs is about 5x10-4g for rootsand 10-3g for shoots. A more accurate experiment on the threshold acceleration willbe performed on the International Space Station (ISS) in the context of the EuropeanModular Cultivation System (EMCS) project.

So far, the main result obtained in space relates to gravity sensing and the mode ofaction of statoliths. It has been shown that the cytoskeleton is intimately involved inthe perception of gravity. The analysis of statocyte polarity in space showed that thestatoliths were principally located in the centre of the cell (statocyte), close to thenucleus. The transfer from gravity to microgravity induces a movement of theamyloplasts towards the cell centre. This finding has led to a new hypothesisconcerning the signal transduction of the gravity stimulus. According to this, thestatoliths could exert a tension on the biopolymer actin network of the cell, whichbecomes asymmetrical when the organ is placed horizontally.

Although the nature of the gravity sensors is still disputed, it must be recognised thatspace experiments have provided new data about gravity sensing, causing plantphysiologists to change their views on how plants sense gravity. It must also be notedthat space experiments on gravitropism were always performed in parallel with activeground-based research and that space was also a driver in this field. Space experiments

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2.2.3 Exobiology: The Origin, Evolution and Distribution of Life

A. Brack


Exobiology, in its broader definition, includes the study of the origin, evolution anddistribution of life in the Universe. Although it is difficult to define what is meant by theterm 'primitive life', one generally considers as living any chemical system able, as aminimum, to transfer its molecular information via self-reproduction and to evolve.The concept of evolution implies that the chemical system normally transfers itsinformation fairly faithfully, but makes a few random errors. These may lead topotentially higher complexity and possibly to better adaptation to the existingenvironmental constraints.

Due to this process of evolution acting over several billion years, existing life mustdiffer considerably from the original primitive life forms. Consequently, onlyhypothetical descriptions of primitive life can be proposed. Also, because of thelimitations of time, the prebiotic chemistry that may have led to those primitive lifeforms can never be fully repeated in the laboratory. Therefore, laboratory simulationsmay only represent possible support for plausible hypotheses. The only way aroundthis difficulty is to collect clues from different disciplines.

Today, many data related to the history of terrestrial life, as well as to possible nichesfor extraterrestrial life, have been collected by scientists in astronomy, planetology,geology, paleontology, biology and chemistry. These data are like the pieces of a jigsaw puzzle that can now be put together to give a clearer picture of the possibledistribution of life in the Universe (see next page).

2.2.3.2 The Origins of Terrestrial Life

By analogy with contemporary life, it is generally believed that primitive life originatedfrom the processing of reduced organic molecules by liquid water.

- The Primitive Earth

Liquid water is considered to be one of the prerequisites for life to appear and evolveon a planet. Water molecules are widespread in the Universe, as grains of solid ice oras very dilute water vapour. By contrast, liquid water is a fleeting substance, which


Further Reading

Claassen D.E. & Spooner B.S. 1994, Impact of altered gravity on aspects of cell biology,Int. Rev. Cytol. 156, pp. 301 – 373.

Evans L., Moore R. & Hasenstein K.-H. 1986, How roots respond to gravity, Sci. Am.,255, pp. 100 – 107.

Halstead T.W. & Dutcher F.R. 1987, Plants in Space, Ann. Rev. Plant Physiol. 38, pp. 317 – 345.

Krikorian A..D. & Levine H.G. 1991, Development and growth in space. In: PlantPhysiology, a Treatise, Vol. X, Academic Press, London, pp. 491 – 555.

Merkys A.J. & Laurinavicius R.S. 1990, Plant growth in space. In: Fundamentals ofSpace Biology (Eds. M. Ashima & G.M. Malacinski), Japan Sci. Soc. Press, Tokyo/Springer Verlag, Berlin, pp. 69 – 83.

Musgrave M.E., Kuang A. & Porterfield D.M. 1997, Plant reproduction in spaceflightenvironments, Gravitational and Space Biology Bulletin, 10, pp. 83 – 90.

Sack F.D. 1991, Plant gravity sensing, Int. Rev. Cytol., 127, pp. 193 – 252.

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frozen. The size of the Earth and its distance from the Sun are such that our planetnever experienced either a runaway greenhouse or divergent glaciation.

- Prebiotic Formation of Small Molecules

Present-day life is based upon organic molecules made of carbon, hydrogen, oxygen,nitrogen, sulphur and phosphorus atoms. Originally, the carbon needed to constructthe molecules of life was available as simple volatile compounds, either reduced asmethane or oxidised as carbon monoxide or carbon dioxide.

Synthesis in the AtmosphereIn 1924, the Russian biochemist Aleksander Oparin suggested that the small, reducedorganic molecules needed for primitive life were formed in a primitive atmospheredominated by methane. This idea was tested in the laboratory by Stanley Miller in 1953.He exposed a mixture of methane, ammonia, hydrogen and water to electric discharges,to mimic the effects of lightning. Among the compounds formed, he identified four of thetwenty naturally occurring amino acids, the building blocks of proteins. Since this historicexperiment, seventeen natural amino acids have been obtained via the intermediateformation of simple precursors such as hydrogen cyanide and formaldehyde. It has beenshown that spark-discharge synthesis of amino acids occurs efficiently when a reducinggas mixture containing significant amounts of hydrogen is used. However, the truecomposition of the primitive Earth's atmosphere remains unknown. Today, geochemistsfavour a non-reducing atmosphere dominated by carbon dioxide. Under such conditions,the production of amino acids appears to be very limited.

Synthesis in Oceanic Hydrothermal VentsDeep-sea hydrothermal systems may also be likely environments for the synthesis ofprebiotic organic molecules and perhaps even for primitive life. Amino acids have beenobtained, although in low yields, under conditions simulating these hydrothermalvents. Hydrothermal vents are often disqualified as efficient reactors for the synthesisof bio-organic molecules, because of the high temperatures. However, the productsthat are synthesized in hot vents are rapidly quenched in the surrounding cold water,which may preserve those organics formed.

Extraterrestrial Delivery of Organic Molecules to the EarthBesides abundant H and He, 114 interstellar and circumstellar gaseous molecules arecurrently identified in the interstellar medium. Ultraviolet irradiation of cosmic dustgrains may result in the formation of complex organic molecules or even totalcarbonization of the sample, forming, according to the local environmental conditions,carbonaceous matter such as amorphous carbon, hydrogenated amorphous carbonor coal- and kerogen-like materials. The incorporation of such interstellar matter intometeorites and comets in the earliest stages of the evolution of the Solar Systemprovides the basis for the cosmic dust connection.


can persist only above 0˚C and under an atmospheric pressure higher than 6 mbar.Therefore, the mass of a planet and its distance from the star are two basiccharacteristics that will determine the presence of liquid water.

If a planet is too small, like Mercury or the Moon, its small gravitational field will notbe able to retain any atmosphere and, therefore, any liquid water. If the planet is tooclose to the star, the mean surface temperature rises, due to starlight intensity. Anyseawater present would evaporate, delivering large amounts of water vapour into theatmosphere and thus contributing to the 'greenhouse effect'. This, in turn, causes afurther temperature rise. Such a positive feedback loop could lead to a runawaygreenhouse, where all of the surface water would be transferred to the upperatmosphere. There, photo-dissociation by ultraviolet light would break the moleculesdown into hydrogen and oxygen. Loss of the atmosphere would eventually result, dueto the escape of hydrogen to space and the combination of oxygen with the crust. If aplanet is far from the star, it may permit the existence of liquid water, provided that itcan maintain a constant greenhouse atmosphere. However, water could provoke itsown disappearance. The atmospheric greenhouse gas CO2, for instance, would bedissolved in the oceans and finally trapped as insoluble carbonates by rock-weathering. This negative feedback could lower the surface pressure andconsequently the temperature to such an extent that any water would be largely

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LIFE IN THE UNIVERSE

Terrestrial Life as the Reference Extraterrestrial Life

Origins of life

Relics of primitive life

Limits of life Life in the Solar System

Panspermia

Extrasolar life

• the primitive Earth• prebiotic formation

of small molecules • life in a test tube

• fossil bacteria• oldest sediments• one-handedness

• temperature• salt• pH• pressure• deep subsurface

extrasolar planets •spectral signature of extrasolar life •

bacterial life in space •interplanetary transfer of life •

life on Mars and •

life on Europa •organic chemistry on Titan •

SNC meteorites

These excesses may help us to understand the emergence of a 'one-handed life'. Forexample, proteins are built up with twenty different amino acids. Each amino acid,with the exception of glycine, exists in two mirror-image forms, L and D. But theproteins of life actually use only the L-form amino acids. Proteins adopt asymmetricalrigid geometries, right-handed alpha-helices and beta-sheets, which play a key role inthe catalytic activity. The excess of the one-handed amino acids, as found in thisparticular meteorite, may be the result of stellar radiation acting on the organicmantles of the cosmic dust grains from which the meteorite was originally formed.

Analysis of dust collected in the Greenland and Antarctic ice sheets shows that theEarth captures interplanetary dust as micro-meteorites at a rate of about 50 – 100tons per day.

About 99% of this mass is carried by micro-meteorites in the 50 – 500 µm size range.This value is much higher than the most reliable estimate of the normal meteorite flux,which is about 0.03 tons per day. A high percentage of micro-meteorites, from 50 to100 µm in size, have been observed to be unmelted, indicating that a large fractionentered the terrestrial atmosphere without drastic thermal alteration. In this sizerange, the carbonaceous micro-meteorites represent 80% of the samples and contain2% of carbon, on average.

This flux of incoming micro-meteorites might have brought to the Earth about 1020 grammes of carbon over a period of 300 million years, corresponding to the lateterrestrial bombardment phase. This delivery represents more carbon than thatengaged in the present surficial biomass, i.e. about 1018 grammes. Amino acids, such


The ESA Infrared Space Observatory (ISO) has provided extraordinary resultsconcerning the nature of these cosmic dust particles. ISO’s spectroscopy has alloweda new definition of the composition of interstellar ices, thermal processing in theprotostellar vicinity and gas-grain chemistry. A comparison of interstellar andcometary ices, using ISO data, has revealed important similarities between interstellarices and volatiles measured in the comas of some comets. The link between theprocesses occurring in these dense clouds of interstellar dust and molecules and thecomets seems now to be clearer. Studies of the connection between interstellar,cometary and meteoritic dust provide important constraints on the formation of theSolar System and early evolution on Earth.

Comets show substantial amounts of organic material, as was nicely demonstrated byESA’s Giotto mission in 1986. On average, dust particles ejected from Comet Halley’snucleus contain 14% organic carbon by mass. About 30% of cometary grains aredominated by the light elements C, H, O, and N, and 35% are close in composition tothe carbon-rich meteorites. Among the molecules identified in comets are hydrogencyanide and formaldehyde. The presence of purines, pyrimidines, and formaldehydepolymers has also been inferred from the fragments analyzed by Giotto’s Picca andVega’s Puma mass-spectrometers. However, there is no direct identification of thecomplex organic molecules present in the cosmic dust grains and in the cometarynucleus.

Many chemical species of interest for exobiology were detected in Comet Hyakutakein 1996, including ammonia, methane, acetylene, acetonitrile and hydrogenisocyanide. In addition, Comet Hale-Bopp was also shown to contain methane,acetylene, formic acid, acetonitrile, hydrogen isocyanide, isocyanic acid,cyanoacetylene, and thioformaldehyde. It is possible, therefore, that cometary grainsmight have been an important source of organic molecules delivered to the primitiveEarth.

The study of meteorites, particularly the carbon-rich ones known as ‘carbonaceouschondrites’ that contain up to 5% by weight of organic matter, has allowed closeexamination of the extraterrestrial organic material that has been delivered to theEarth. Eight proteinaceous amino acids have been identified in one such meteorite,among more than 70 amino acids found therein. These amino acids are asymmetric.

The two enantiomers, L and D (mirror-image geometrical configurations of the sameamino acid), are generally found in equal proportions. However, a 9% excess of L-amino acids has recently been measured in that particular meteorite. The presenceof this excess points towards an extraterrestrial process of asymmetric synthesis ofamino acids, an asymmetry that is then preserved inside the meteorite, and in thiscase delivered to the Earth.

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Figure 2.2.3.1. Each amino acid – with the exception of glycine – is asymmetrical andcould exist as either of two non-superimposable mirror images, called ‘enantiomers L andD’. Only the L-amino acid enantiomers are found in proteins on Earth

carbonaceous meteorites discussed above. However, the membranes obtained withthese simple amphiphiles are not stable over a broad range of conditions. Stableneutral lipids can be obtained by condensing fatty acids with glycerol or with glycerolphosphate, thus mimicking the stable contemporary phospholipid.

Most of the chemical reactions in a living cell are achieved by proteinaceous enzymes,made of 20 different L-amino acids. Amino acids were most likely available on theprimitive Earth as complex mixtures. Chemical reactions able to selectively condensethe protein amino acids, at the expense of the non-protein ones in water, have beenidentified by the author. Helical and sheet-structures can be modelled with the aid ofonly two different amino acids, one hydrophobic, the second hydrophilic. Polypeptideswith alternating hydrophobic and hydrophilic residues adopt a water-soluble beta-sheet geometry, because of hydrophobic side-chain clustering. Due to the formation ofa beta-sheet, alternating sequences gain a good resistance to chemical degradation.Aggregation of alternating sequences into beta-sheets is possible only with all-L or all-D polypeptides. Short peptides have also been shown to exhibit catalyticproperties.

In contemporary living systems, the hereditary memory is stored in nucleic acids, longchains built from nucleotides. Each nucleotide is composed of a base (purine orpyrimidine), a sugar (ribose for RNA, deoxyribose for DNA), and a phosphate group.However, the accumulation of significant quantities of natural RNA nucleotides doesnot appear to be a plausible chemical event on the primitive Earth.

The RNA WorldSome ribozymes (RNA) are able to act as catalytic molecules. Since RNA was shown tobe able to act simultaneously as an information and as a catalytic molecule, it hasbeen considered to be the first living system on the primitive Earth. A ribozyme-based'RNA world' has been studied in some detail. One should, however, remember that thesynthesis of RNA itself, under prebiotic conditions, remains an unsolved challenge. Itseems unlikely that life started with RNA molecules, because these molecules are notsimple enough. The RNA world probably appears as an episode in the evolution of life,before the appearance of cellular microbes, rather than as the birth of life itself.

Autocatalytic LifeChemists are now tempted to consider that primitive replicating systems must haveused simpler information-retaining molecules than biological nucleic acids or theiranalogues. They are looking for simple self-sustaining chemical systems capable ofself-replication, mutation, and selection. It has been shown that simple molecules,unrelated to the nucleotides, can actually provide exponentially replicatingautocatalytic models. Beautiful examples of autocatalytic micelle growth have beendemonstrated. However, these autocatalytic systems do not really store hereditarymemory and cannot therefore evolve by natural selection.


as α-amino isobutyric acid,have recently been identi-fied in these Antarcticmicro-meteorites. Thesegrains also contain a high proportion of metallic sulphides, oxides, and clay mineralsthat belong to various classes of catalysts. In addition to the carbonaceous matter,micro-meteorites might also have delivered a rich variety of catalysts, having perhapsacquired specific crystallographic properties during their synthesis in the microgravityenvironment of the early solar nebula. They may have functioned as tiny chemicalreactors when reaching oceanic water.

Amino acids like those detected in the carbonaceous meteorites have been exposedfor 10 days to the space conditions of Earth orbit, using the unmanned Russiansatellites Foton-8 and Foton-11, and for three months with the Mir station (Perseusexperiment). The amino acids were both free and associated with a mineral powder.Analyses run after the flights by the Exobiology Group in Orléans (F) showed thatexposed aspartic acid and glutamic acid were partially photo-processed duringexposure to solar UV. However, decomposition was prevented when the amino acidswere embedded in clays. The main limitations of these experiments were the relativelyweak irradiation of the samples due to the short flight duration, the non-synchronousorbits, and the absence of an automatic Sun-pointing device. The ESA Expose Facility,to be located on the International Space Station, will offer an important opportunityfor long-duration exposure of amino acids and other biogenic molecules.

- Life in a Test Tube

Primitive Cellular LifeBy analogy with contemporary living systems, it is tempting to consider that primitive lifeemerged as a cellular object, requiring boundary molecules able to isolate the systemfrom the aqueous environment (membrane). Also needed would be catalytic molecules toprovide the basic chemical work of the cell (enzymes) and information-retaining moleculesto allow the storage and the transfer of the information needed for replication (RNA).

Fatty acids are known to form vesicles when the hydrocarbon chains contain morethan ten carbon atoms. Such vesicle-forming fatty acids have been identified in the

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Figure 2.2.3.2. Grains collectedfrom Antarctic old blue ice. All

dark grains are micro-meteorites. Only a few of them

(bright spheres) have meltedduring high-speed

atmospheric entry (courtesy ofM. Maurette)

the carbon residues of previously living matter may be identified by this enrichmentin 12C.

A compilation has been made of the carbon isotopic composition of over 1600samples of fossil kerogen (a complex organic macromolecule produced from the debrisof biological matter) and compared with that from carbonates in the samesedimentary rocks. This showed that the biosynthesis by photosynthetic organismswas involved in all of the sediments studied. In fact, this offset is now taken to be oneof the most powerful indications that life on Earth was active nearly 3.9 billion yearsago, because the sample suite encompasses specimens right across the geologicaltime scale. Some organic matter in ancient sediments has been measured as beingeven more enriched in the light isotope of carbon, which would suggest theinvolvement of methane-utilizing organisms.

Unfortunately, the direct clues that could help chemists to identify the molecules thatparticipated in the actual emergence of life on Earth about 4 billion years ago havebeen erased by geological plate tectonics, by the permanent presence of runningwater, by solar ultraviolet radiation and by oxygen produced by life.

- Homochirality: A Geometrical Indicator of Life

Pasteur was probably the first person to realize that the biological asymmetry (one-handedness) discussed earlier could best distinguish between inanimate matter and


2.2.3.3 Relics of Early Terrestrial Life in Geological Records

- Bacteria Microfossils

The earliest morphological fossils occur in rocks from South Africa, dating back 3.3 to3.4 billion years.

Eleven species of cellularly preserved filamentous fossil microbes, comprising theoldest diverse microbial assemblage now known in the geologic record, werediscovered in Northwestern Australia. This assemblage has established thatfilamentous cyanobacterium-like micro-organisms were extant and bothmorphologically and taxonomically diverse at least as early as ~3.465 billion yearsago. It suggests that oxygen-producing organisms that relied upon solar energy andmanufactured their organic constituents from inorganic material, may have alreadyevolved by this early stage in biotic history.

- Oldest Sediments

The isotopic signatures of the organic carbon found in Greenland meta-sedimentsprovide indirect evidence that life may be 3.85 billion years old. Taking the age of theEarth as 4.5 billion years, this means that life began as a quite early event in theEarth's history. This isotopic evidence stems from the fact that the carbon atom hastwo stable isotopes, carbon 12 and carbon 13. The 12C/13C ratio in abiotic mineralcompounds is 89. In biological material, the process of photosynthesis gives apreference to the lighter carbon isotope and raises the ratio to about 92. Consequently,

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Figure 2.2.3.3. Fossilised terrestrial prokaryote (Early Archean 3.3 – 3.4 Ga), South Africa(Courtesy of F. Westall)

Figure 2.2.3.4. A loosely packed conglomerate from the Greenland Isua Suite attesting tothe presence of running water on the terrestrial surface 3.8 Ga ago (courtesy of M. Schidlowski)

Salt-loving organisms, known as ‘extreme halophiles’, have been well-studied. Theytolerate a wide range of salt concentrations (1 – 20% NaCl) and some procaryotes, theextreme halophiles, have managed to thrive in hypersaline biotopes (salines, saltedlakes). They are, in fact, so dependent on such high salt concentrations that theycannot grow (and may even die) at concentrations below 10% NaCl.

The chemistry of life on Earth is optimised for neutral pH. Again, some micro-organisms have been able to adapt to extreme pH conditions, from pH 0 (extremelyacidic) to pH 12.5 (extremely alkaline), albeit maintaining their intracellular pHbetween pH 4 and 9. As with temperature, the intracellular machinery cannot escapethe influence of pressure. However, there are organisms in the deepest parts of theocean where pressures reach 1100 bar. The extreme pressure limit for life on Earth isunknown – environments above 1100 bar have not been explored.

For a long time, it was believed that deep subterranean environments were sterile. Animportant recent development has been the recognition that bacteria actually thrivein the terrestrial crust. Subterranean micro-organisms are usually detected insubterranean oil fields or in the course of drilling experiments. For example, recentresearch has demonstrated that microbes are present much deeper in marinesediments than was previously thought possible, extending to at least 750 m belowthe sea floor, and probably much deeper. To depths of at least 432 m, microbes havebeen identified as altering volcanic glass. These data provide a preliminary, andprobably conservative, estimate of the biomass in this important new ecosystem. Itamounts to about 10% of the surface biosphere.

These discoveries have radically changed the perception of marine sediments andindicate the presence of a largely unexplored deep bacterial biosphere that may evenrival the Earth's surface biosphere in size and diversity. Clearly, this discovery also hasimportant implications for the probability of life existing on other planets in the SolarSystem and elsewhere.

2.2.3.5 The Search for Life in the Solar System

- Life on Mars and the SNC Meteorites

Mars mapping by Mariner-9, Viking-1 and -2 and Mars Global Surveyor revealedchannels resembling dry river beds.

The inventory of the total amount of water that may have existed at the surface ofMars is difficult to estimate and varies from some metres to several hundred metres.Liquid water is generally considered to have been restricted to the very early stages ofMartian history.


life. Life that would simultaneously use both the right- and left-handed forms of thesame biological molecules appears, in the first place, very unlikely for geometricalreasons. Enzyme beta-pleated sheets cannot form when both L- and D-amino acids arepresent in the same chain. Since the catalytic activity of an enzyme is intimatelydependent upon the geometry of the chain, the absence of beta-pleated sheets wouldimpede, or at least considerably reduce, the activity spectrum of the enzymes.

The use of one-handed biomonomers also sharpens the sequence information of thebiopolymers. For a polymer made of n units, the number of sequence combinationswill be divided by 2n when the system uses only homochiral (one-handed) monomers.Taking into account the fact that enzyme chains are generally made up of hundreds ofmonomers, and that nucleic acids contain several million nucleotides, the tremendousgain in simplicity offered by the use of monomers restricted to one-handedness is self-evident. Life on Earth uses homochiral left-handed amino acids and right-handedsugars. A mirror-image life, using right-handed amino acids and left-handed sugars, isperfectly conceivable and might develop on another planet. Thus, homochirality canbe a crucial signature for life.

2.2.3.4 The Limits of Life on Earth

Life on Earth is based upon the chemistry of carbon in water. The temperature limitscompatible with the existence of life are thus imposed by the intrinsic properties of thechemical bonds involved in this type of chemistry at different temperatures. Presently,the maximum temperature limit known for terrestrial organisms is around 113˚C forthe deep-sea microbe Pyrolobus fumarii.

Important factors preventing life at temperatures well above 110˚C are the thermalinstability of some chemical bonds involved in biological molecules and themembrane permeability. Life is extremely diverse in the ocean at temperatures of 2˚C. Living organisms, especially micro-organisms, are also present in the frozen soilsof arctic and alpine environments. Antarctica has a wide range of extreme habitatsand microbial ecosystems developing in dry valley rocks. The lower limit for bacterialgrowth published in the literature is –12˚C, the temperature at which intracellular iceis formed.

In some theoretical scenarios, life appeared at very high temperatures. That meanstoday's hyperthermophiles might be viewed as relics of the last common universalancestor of all living beings. However, this hot-origin-of-life hypothesis has beenseriously disputed, based on the fact that RNA is very unstable at high temperatures.The most attractive hypothesis might be that life appeared in a moderatelythermophilic environment, hot enough to boost catalytic reactions, but cold enoughto avoid the problem of macromolecule thermal degradation.

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glass pockets. Both compositionally and isotopically, this gas matched in all respectsthe makeup of the Martian atmosphere, as measured by the Viking mass-spectrometer. The data provide a very strong argument that at least that particularSNC meteorite came for Mars, the product of a high-energy impact that ejectedmaterial into space.

There are now fourteen SNC meteorites known in total, with EETA79001 andALH84001 supplying new and highly interesting information. A subsample ofEETA79001, excavated from deep within the meteorite, has been subjected tostepped-combustion. The CO2 release from 200 to 400˚C suggested the presence oforganic molecules. The carbon is enriched in 12C, and the carbon-isotope differencebetween the organic matter and the carbonates in Martian meteorites is greater thanthat seen on Earth. This could be indicative of biosynthesis, although some other asyet unknown reason for this enrichment cannot be ruled out. McKay and co-workershave reported the presence of other features that may represent a signature of relicbiogenic activity on Mars, but today this biological interpretation has been almostabandoned.

Because Mars had a warm and wet past climate, its surface must be covered by bothan impact-generated layer and by sedimentary rocks deposited by running and/orstill water. Such consolidated sedimentary hard rocks ought therefore to be foundamong the Martian meteorites. However, no such sedimentary material has beenfound in any SNC meteorite. It is possible that they did survive the effects of the escapeacceleration from the Martian surface, but did not survive terrestrial atmosphericentry, because of deterioration of the cementing mineral.

The STONE experiment flown by ESA is designed to study just such physical andchemical modifications of sedimentary rocks during atmospheric entry from space. Abasalt (in-flight control), a dolomite (sedimentary rock) and an artificial Martianregolith (80% crushed basalt and 20% gypsum) were embedded in the ablative heatshield of Foton-12, which was launched on 9 September and landed on 24 September1999.

The samples collected after this world-first have had their chemistry, mineralogy andisotopic compositions analysed by a European consortium. Atmospheric infallmodifications are made visible by reference to the untreated samples. The resultssuggest that some Martian sediments could partially survive terrestrial atmosphericentry from space.

Even if the evidence for ancient life in ALH84001 is not established, the two SNCmeteorites do show the presence of organic molecules. This suggests that theingredients required for the emergence of a primitive life form may have been presenton the surface of Mars. Therefore, it is tempting to consider that micro-organisms may


Mars therefore possessed an atmosphere capable of decelerating carbonaceous micro-meteorites, and chemical evolution may have been possible. The Viking-1 and -2lander missions were designed to address the question of extant (rather than extinct)life on Mars. Three experiments were selected to detect metabolic activity such asphotosynthesis, nutrition and respiration of potential microbial soil communities.Unfortunately, the results were ambiguous because although ‘positive’ results wereobtained, no organic carbon was found in the Martian soil by gas-chromatography/mass-spectrometry. It was concluded that the most plausibleexplanation for these results was the presence at the Martian surface of highlyreactive oxidants, like hydrogen peroxide, which would have been produced photo-chemically in the atmosphere. The Viking lander could not sample soils below 6 cm,and therefore the depth of this apparently organic-free and oxidising layer is unknown.Direct photolytic processes can also be responsible for the dearth of organics at theMartian surface.

Although the Viking missions were disappointing for exobiology, in the long run theprogramme has proved to be extremely beneficial for investigating the possibility oflife on Mars. Prior to Viking, it had been apparent that there was a small group ofmeteorites, all of igneous (volcanic) origin, known as the ‘SNC’ (after their typespecimens Shergotty, Nakhla and Chassigny) that had comparatively youngcrystallisation ages, equal to or less than 1.3 billion years. One of these meteorites,designated EETA 79001, was found in Antarctica in 1979. It had gas trapped within

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Figure 2.2.3.5. A portion of the meandering canyons of the Martian Nanedi Valles systemviewed by Mars Global Surveyor (courtesy of Malin Space Science Systems/NASA)

from freezing by tidal heating as a result of the variation in gravitational field acrossthe body of the satellite. Heat transfer from the core to the bottom of the ocean, similarto thermal vents in terrestrial oceans, is another possible source of thermal energy.Although the existence of such an ocean is still uncertain, the last images from Galileoshowing evidence for mobile icebergs support the presence of liquid water at shallowdepths below the surface, either today or at some time in the past.

If liquid water is present within Europa, it is quite possible that it includes organicmatter derived from thermal vents. Terrestrial-like prebiotic organic chemistry andprimitive life may therefore have developed in Europa's ocean. If Europa maintainedtidal and/or hydrothermal activity in its subsurface until now, it is possible thatbacterial activity is still present. Thus, the possibility of extraterrestrial life beingpresent in a subsurface ocean on Europa must be taken seriously. The most likely sitesfor extant life would be at hydrothermal vents below the most recently resurfacedarea. To study this directly would require making a borehole through the ice in orderto deploy a robotic submersible. On the other hand, biological processes in andaround hydrothermal vents could produce biomarkers that would appear as traces incryo-volcanic eruptions and thereby be available at the surface for in-situ analysis orsample return. Mineral nutrients delivered through cryo-volcanic eruption wouldmake the same locations the best candidates for photosynthetic life.


have developed on Mars untilliquid water disappeared. SinceMars probably had no platetectonics, and since liquid waterseems to have disappeared fromMars’ surface very early on, theMartian subsurface perhapscontains a frozen record of veryearly forms of life.

NASA has planned a very intensiveexploration of Mars, and Europeanand Japanese missions are also taking place. Exobiology interests are included,especially in the analysis of samples from sites where the environmental conditionsmay have been favourable for the preservation of evidence of possible prebiotic orbiotic processes. ESA has convened an Exobiology Science Team to design a multi-userintegrated suite of instruments for the search for evidence of life on Mars. Priority hasbeen given to the in-situ organic and isotopic analysis of samples obtained bysubsurface drilling. A first exobiology lander, called ‘Beagle-2’, is expected to belaunched in June 2003, as part of the ESA Science Directorate’s Mars Express mission.

- Life within Europa's Ocean?

Europa appears one of the most enigmatic of the Galilean satellites. With a meandensity of about 3.0 gcm-3, the Jovian satellite should be dominated by rocks. Ground-based spectroscopy, combined with gravity data, suggests that the satellite has an icycrust kilometres thick and a rocky interior. The Voyager images showed very fewimpact craters on Europa's surface, indicating recent, and probably continuing,resurfacing by cryo-volcanic and tectonic processes.

The Voyager spacecraft also revealed that Europa's surface is crossed by numerousintersecting ridges and dark bands. It has been suggested that Europa's outer ice shellmight be separated from the silicate interior by a liquid water layer, which is prevented

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Figure 2.2.3.6. The STONE experimentmounted on the re-entry heat shield of

the Foton capsule. The samples were ofdifferent compositions: one represented

a possible Martian regolith material,another was a normal sedimentary

rock. A basalt was used as a control.The goal was to see if sedimentary rock

materials can withstand high-velocityentry into the Earth's atmosphere

Figure 2.2.3.7. A Galileo image of an 80 km x 95 km area of Europa, where the youngestfeatures are domes that are probably viscous cryo-volcanic flows or sites of shallowintrusion – good targets for the search for traces of life (courtesy of NASA)

exposure to space vacuum for extended periods, provided they are shielded againstthe intense solar UV radiation. Most results are available from spores of the bacteriumBacillus subtilis. If shielded against UV, spores survive for at least six years in space,the maximum period of exposure tested so far. Space experiments have also shownthat up to 70% of bacterial and fungal spores (a dormant form) can survive short-term(e.g. 10 days) exposure to space vacuum, even without any protection. The chances ofsurvival in space are increased if the spores are embedded in chemical protectantssuch as sugars or salt crystals, or if they are exposed in thick layers. For instance,about 5% of a species of the extreme halophile Haloarcula survived a two weeks ofspace exposure on a Foton flight.

Solar UV radiation has been found to be the most deleterious factor in space, as testedwith dried preparations of viruses, bacterial and fungal spores, with DNA being themost lethal target.

The radiation field in the Solar System is governed by components of galactic andsolar origin. It is composed of electrons, alpha-particles and cosmic heavy ions, thelatter being the most ionising and therefore the most damaging components. Theheavy particles of cosmic radiation are conjectured to set the ultimate limit on thesurvival of spores in space because they penetrate even heavy shielding. Themaximum time for which a spore can escape a hit by a heavy particle has beenestimated to be 105 – 106 years.

During the major part of a hypothetical journey through deep space, micro-organisms areconfronted with the 4 K cold emptiness. Laboratory experiments under simulatedinterstellar-medium conditions point to a remarkably less damaging effect of UV radiationat these low temperatures. Treating B. subtilis spores with three simulated factorssimultaneously (UV, vacuum and 10 K temperature) produces an unexpectedly highsurvival rate, even at very high UV fluxes. From these data, it has been estimated that, inthe most general environment in space, spores may survive for hundreds of years.

- Interplanetary Transfer of Life

Although it will be difficult to prove that life can be transported through the SolarSystem, the chances of the different steps in the process occurring can be estimated.These include: (1) the escape process, i.e. the removal to space of biological materialthat has survived being lifted from the surface to high altitudes; (2) the interim state inspace, i.e. the survival of the biological material over time scales comparable withinterplanetary passage; (3) the entry process, i.e. the non-destructive deposition of thebiological material on another planet.

The identification of some meteorites as being of lunar origin and some others as mostprobably being of Martian origin, shows that the escape from a planet of material


- Organic Chemistry of Titan

Titan's atmosphere was revealed mainly by the Voyager-1 mission in 1980, whichyielded its bulk composition: 90% molecular nitrogen and about 1 – 8% methane.Also, a great number of trace constituents were observed in the form of hydrocarbons,nitriles and oxygen compounds, mostly CO and CO2. Titan is the only other object inour Solar System to bear a resemblance to our own planet in terms of atmosphericpressure (1.5 bar) and carbon/nitrogen chemistry. It therefore represents a naturallaboratory for studying the formation of complex organic molecules on a planetaryscale and over geological times.

The ISO satellite has detected tiny amounts of water vapour in the higher atmosphere,but Titan's surface temperature (94 K) is much too low for the presence of liquid water.Although the latter is totally absent, the satellite provides a unique milieu to study, in- situ, the products of the fundamental physical and chemical interactions driving aplanetary organic chemistry. Titan also serves as a reference laboratory for studying,by default, the role of liquid water in exobiology.

The NASA/ESA Cassini-Huygens spacecraft launched in October 1997 will arrive in thevicinity of Saturn in 2004 and perform several flybys of Titan, making spectroscopic,imaging, radar and other measurements. The Huygens descent probe, managed byEuropean scientists, will penetrate Titan’s atmosphere and systematically study theorganic chemistry in Titan's geofluid. For 150 minutes, in-situ measurements willprovide detailed analysis of the organics present in the air, in the aerosols and at thesurface.

2.2.3.6 Panspermia: The Distribution of Life

- The Survival of Microbes in Space

In order to study the survival of resistant microbial forms in the upper atmosphere andfree space, microbial samples have been exposed in-situ aboard balloons, rockets andspacecraft. The ESA Microgravity Programme has continued to support experimentsof that type. A priori, the space environment seems to be very hostile to life. This is dueto the high vacuum, intense radiation of galactic and solar origin, and extremetemperatures. In the endeavour to disentangle the network of potential interactions ofthe parameters of space, methods have been applied to isolate each parameter and toinvestigate its impact on biological integrity, applied singly or in controlledcombinations.

Space vacuum has been considered to be one of the factors that may preventinterplanetary transfer of life because of its extreme dehydrating effect. However,experiments in space have demonstrated that certain micro-organisms can survive

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proposing the construction of a five-telescope infrared interferometer to study theatmospheres of exoplanets. The mission, known as ‘IRSI-Darwin’, is presently understudy by ESA. The detection of an unambiguous electromagnetic signal (via the SETIprogramme) would obviously be the most exciting event, but remains problematic.

2.2.3.8 Conclusion

Is there life elsewhere? Recent discoveries have allowed a better estimate of thechances of discovering an extraterrestrial life form. Biologists have shown thatbacterial life can survive under extreme conditions. Life has continued to develop verywell in water that is very acidic, alkaline, or is a strong brine solution. It has alsosurvived and flourished in water at high pressure and at temperatures above 100˚C. A flourishing biosphere has been discovered a kilometre below the Earth’s surface.

Primitive terrestrial life probably relied on extraterrestrial organic molecules, made inthe interstellar medium and delivered to the Earth by cometary grains. Such an importprocess only required an atmosphere to decelerate the particles. Such an atmosphereexisted 4 billion years ago, as attested to by the presence of liquid water at the Earth’ssurface. As a consequence, any planet harbouring liquid water at its surface can beconsidered a potential site for the emergence of life.

There is clear evidence that water existed in substantial amounts on the surface of Marsat some earlier epoch. Therefore, primitive life might also have developed there. How longwater was present at the Martian surface is not known. Nor is it yet certain if water stillexists in subsurface aquifers, although there are clear indications of the existence of largepermafrost regions and of old water flows out of associated areas. Given the discovery ofa flourishing biosphere even a kilometre below the Earth’s surface, it would seem possiblethat a similar microbial community might still be present below the surface of Mars,having long ago retreated into that ecological niche following the disappearance of asurface-water environment. The possibility that life may have evolved on Mars during anearly period when there was water on its surface and that life may still exist deep belowthe surface, makes it a prime candidate in the search for life beyond the Earth.

Some of the organic molecules that participated in the emergence of life might alsohave been made in hydrothermal oceanic vents. Europa may have an ocean of liquidwater beneath its icy crust, as suggested by both data and theory. If submarinevolcanism exists on Europa, the question arises as to whether such activity couldsupport life, as do volcano-hydrothermal sites on the Earth's sea floor.

Organic chemistry has been shown to be universal, since over eighty different organicmolecules have been identified in the interstellar medium by radio astronomers. Extra-solar planets have also been discovered, which begins to raise the future possibility ofdetecting water-harbouring planets beyond the Solar System.


ranging from small particles to boulders, after it has suffered a high-energy impact, isclearly a feasible process. In that context, it is also interesting to note that bacterialspores can survive shock waves produced by a simulated meteorite impacts and hugeaccelerations.

Concerning the subsequent survival of life forms during the interim voyage throughspace, it has so far only been possible to observe directly the influence of exposure ofbacterial spores to space for a maximum period of six years. The high survival rate ofthese spores and the high UV-resistance of micro-organisms at the low temperaturesof deep space are interesting results. However, travelling from one planet to another,e.g. from Mars to Earth, by chance requires an estimated mean time of several 105 –106 years for boulder-sized rocks. Periods of only a few months have been calculatedfor the case of microscopic particles. Evidently, more data on the long-term effects inspace are required to allow meaningful extrapolation to the time spans required forthe interplanetary transport of life.

ESA has initiated the development of an exposure facility ‘Expose’, to be attached toan Express Pallet on the truss structure of the International Space Station (ISS). Thiswill allow extensive study of bacterial survival in space.

2.2.3.7 Life Beyond the Solar System

- Exoplanets

New planets have been discovered beyond the Solar System. On 6 October 1995, thediscovery was announced of an extrasolar planet orbiting an 8 billion year old starcalled 51 Pegasus, forty-two light years away within the Milky Way. The suspectedplanet takes just four days to orbit the star. It has a surface temperature of about1000˚C and a mass about half that of Jupiter. One year later, seven other extrasolarplanets were identified. One of them, 47 Ursa Major, has a surface temperatureestimated to be around that of Mars (–90 to –20˚C), and another, 70 Virginis, has asurface temperature estimated at 70 – 160˚C. The latter is the first known extrasolarplanet whose temperature might allow the presence of liquid water. So far, about 30exoplanets have been identified.

- Spectral Signatures of Life

Extra-solar life will not be accessible by space missions in the forseeable future. Theformidable challenge to detect distant life must therefore be tackled by astronomersand radio-astronomers. The detection of water and ozone (an easily detectable tell-talesignature of oxygen) in the atmosphere will be a strong indication, but not an absoluteproof. Other anomalies in the atmospheres of telluric exoplanets, such as the presenceof methane, could be the signature of extra-solar life. European astrophysicists are

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The search for life elsewhere in the Solar System remains one of the great scientificendeavours of our age. The Beagle-2 mission destined to land on Mars represents amilestone for Europe on the road towards that objective, and one that must surely befollowed by other, more ambitious European attempts to probe deep below the surfaceof Mars, to find the relics of an earlier life form or, just possibly, a novel living world.

Further Reading

Brack A. (Ed.) 1998, The Molecular Origins of Life: Assembling Pieces of the Puzzle,Cambridge University Press, Cambridge, UK.

Brack A. 1999, Life in the Solar System, Adv. Space Res. 24, No. 4, pp. 417 – 433.

Brack A., Fitton B., Raulin F. & Wilson A. (Eds.) 1999, Exobiology in the Solar Systemand the Search for Life on Mars., ESA Special Publication SP-1231, October 1999.

Bonner W.A. 1991, The origin and amplification of biomolecular chirality, Origins LifeEvol. Biosphere, 21, pp. 59 – 111.

De Duve Ch. 1991, Blue-print for a Cell: The nature and origin of life, Neil PattersonPub., Burlington, NC, USA.

Delsemme A. 1998, Our Cosmic Origins – From the Big Bang to the Emergence of Lifeand Intelligence, Cambridge University Press, Cambridge, UK.

Horneck G. 1995, Exobiology, the study of the origin, evolution and distribution of lifewithin the context of cosmic evolution: A review, Planet. Space Sci., 43, pp. 189 – 217.

Irvine W.M. 1998, Extraterrestrial organic matter: a review, Origins Life Evol. Biosphere,28, pp. 365 – 383.

Jakosky B. 1998, The Search for Life on Other Planets, Cambridge University Press,Cambridge, UK.

Miller S.L. &. Orgel L.E. 1974, The Origins of Life on Earth, Prentice-Hall, Inc., EnglewoodCliffs, NJ, USA.

Westall F. et al. 2000, An ESA study for the search for life on Mars, Planet. Space Sci.,48, pp. 181 – 202.

Wills Ch. & Bada J. 2000, The Spark of Life - Darwin and the Primeval Soup, PerseusPublishing, Cambridge, MA, USA.


The distribution of life in the Universe may even be favoured by the migration of lifethrough space, a notion known as ‘panspermia’. Recent discoveries that have givennew support to this idea include: (i) The identification of meteorites of lunar and probably also of Martian origin.(ii) The probability of small particles reaching escape velocities through the impact of

large bodies on a planet.(iii) The ability of bacterial spores to survive the shock waves of a simulated high-

energy impact.(iv) The high UV-resistance of micro-organisms at the low temperature of deep space.(v) The high survival rates of bacterial spores over extended periods in space, provided

they are shielded against the intense solar ultraviolet radiation or are coated witha mantle of absorbing material that attenuates it.

The probability that primitive life developed without reliance upon the large complexmolecules of its later evolution, such as RNA, would likely increase the chances ofsurvival of such organisms if ejected into space.

On Earth, life probably appeared about 4 billion years ago, when some organicmolecules processed by liquid water began to transfer their chemical information andto evolve by making a few accidental transfer errors. Schematically, the prebioticconditions can be compared to the parts of a robot. By chance, some parts wereassembled to form a robot able to assemble other parts to form a second identicalrobot, etc. Sometimes, a minor error in the process generated more efficient robots.

The number of parts required for that first robot is still unknown. The problem is that,on Earth, those earliest parts have been erased by plate tectonics, by the permanentpresence of liquid water, by solar ultraviolet radiation, and by life itself. If the numberwas small, life has a real chance of establishing itself on any body presentingenvironmental conditions similar to those that prevailed on the primitive Earth,because simple chemistry is reproducible.

If the number of parts was very large, then life is probably a very rare event, perhapseven restricted to the Earth. Primitive life is expected to have been simple because itappeared when the Earth was constantly being heavily bombarded. A simple self-reproducing system would have been more robust and offered a better chance ofresisting the cataclysmic impacts that probably periodically sterilised the Earth duringthe heavy bombardment. Taken together, all these data strongly support thehypothesis that life is probably not restricted to the Earth.

Looking to the future, the search for the origins of life and its existence elsewhere willbenefit from new and extended space observations using the International SpaceStation. It is important to understand better the limits to the survival of simpleorganisms in space, in order to decide if life on Earth originated from elsewhere.

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Zubay G. 2000, Origin of Life on Earth and in the Universe, Harcourt/Academic Press,Burlington, MA, USA.

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2.3 PHYSICAL SCIENCES AND APPLICATIONS

2.3.1 Macromolecular Crystallisation

J.M. Garcia-Ruiz, J. Drenth, M. Riès-Kautt & A. Tardieu


Biological macromolecules such as proteins, lipids, nucleic acids, carbohydrates andviruses (and their assemblies) are central to living systems. Understanding themechanisms of life is not only a matter of knowing the function that each of thesemacromolecules performs, but also of knowing how they perform it, i.e. of finding outthe relationships between the intimate structure of these molecules and the differenttypes of function that they perform. The success of molecular biology in decipheringthe mechanisms by which certain important macromolecules perform their biologicalroles has awakened the interest of pharmaceutical, medical and food companies andresearch institutions, and has triggered the establishment of some of today’s largestscientific research programmes, like genomics and proteomics.

Crystallisation enters onto the scene because the structure of macromolecules largerthan about 20 kDalton can be only determined from the X-ray diffraction of theircrystals. Therefore, most advanced molecular-biology projects face not only thetedious and complex isolation and purification of the macromolecules, but also theircrystallisation, for which there is not yet a rationale. Many macromolecules arereluctant to crystallise, or when they do so the internal order of the crystallinearrangement is not good enough to provide X-ray diffraction data at the resolutionrequired to establish structure–function correlations. This, linked with the usual smallamount of purified protein available for crystallisation trials, makes crystallisation acritical step.

It is now well-established that macromolecular crystals grow from solutions by thesame mechanisms employed by small inorganic and organic molecules. Experimentalevidence for screw dislocations, two-dimensional nucleation, direct accretion andthree-dimensional nucleation, has been obtained by Michelson interferometry, atomic-force microscopy, electron microscopy, and X-ray topography. The driving force formacromolecular crystallisation is also achieved in the same way as for solutions of


has a significant enhancement of the maximum resolution level been experimentallymeasured and reported.

The very limited flight opportunities for European experiments made it advisable todiscard this strategy, which was mostly based upon crystallisation screening withblind experiments (only 426 ESA protein crystallisation experiments have so far beenperformed, compared with over 7600 by NASA). ESA’s Expert Group on ProteinCrystallisation correctly recommended that more careful attention should be paid tothe fundamental reasons for the plausible benefits of the gravity-less scenario, usingmonitored experiments wherever possible. Thanks to this new strategy, in the last fiveyears a number of new results have been produced, either through on-ground or spacebased research, that allow a better understanding of the problem of macromolecularcrystallisation and the inconsistency of the effects observed for space experiments.The results of these investigations will be summarised here.

2.3.1.2 The Concentration Depletion Zone

Certainly, microgravity sensu-strictum, i.e. 10-6 times the value of gravity on Earth,inhibits buoyancy-driven convection and sedimentation of the growing crystals. Inprinciple, that has important consequences for the critical processes taking place atthe crystal/solution interface.

Crystals grow from solutions by accretion of growth units of the solute. Naturally, aConcentration Depletion Zone (CDZ) is immediately formed around the growingcrystal. Within this region, the solute concentration changes from the concentration inthe bulk solution CINFIN to the concentration of solute at the crystal face Ci. On theground, the very existence of the concentration depletion zone unavoidably createsdensity gradients that trigger the mechanisms of convective flow.

Under microgravity conditions, where the mass transport is controlled by diffusion,the concentration profile in the CDZ varies with time as the crystal grows. Thatvariation is controlled by the balance between the flow of growth units towards thecrystal face and the rate of incorporation of these growth units into the crystal lattice.The kinetics of incorporation at the crystal surface are linked to the bond distributionof the crystallographic structure and are measured by the coefficient βface, while theflow towards the crystal face is highly dependent upon the mass-transport propertiesin the bulk solution. The competition between surface kinetics and diffusion transportis measured by the relation β δ/D, where δ is the width of the CDZ and D is thediffusion coefficient of the macromolecule. When β δ/D << 1, the crystal growth iscontrolled by the processes taking place at its surface. The growth rate is independentof crystal size, which increases linearly with time. However, when β δ/D >> 1, masstransport is the rate-controlling parameter and crystal size increases with the squareroot of time.


small molecules, i.e. by (a) thermal changes, (b) solubility reduction, (c) chemicalreaction, and (d) evaporation.

The techniques employed for protein crystallisation are basically the same, with smallvariations, as those developed in the past for the crystallisation of soluble and slightlysoluble compounds of small molecules. However, macromolecules show somepeculiarities, which need to be considered in what follows because they rendercrystallisation a difficult challenge:

1. Macromolecules display a rather asymmetric and weak bonding configuration attheir surfaces. This, together with their large size, makes attachment at the correctcontact points less probable for growth units landing on the crystal surface.

2. They tend to aggregate in n-mers, which diversifies the possible shapes and sizesof growth units, making the ordered accretion of growth units more complex.

3. Typically, macromolecular solutions contain considerable amounts of contaminants,even after thorough purification. The incorporation of impurities during the crystalgrowth process is an additional source of problems in the crystallisation of proteins.

4. Because of the large molecular size, and also the small number of moleculescomprising the critical nuclei, the nucleation process typically takes place outsidethe expected window for classical nucleation theories. Thus, under somecircumstances, biological macromolecules have properties resembling colloids,rather than small molecules, e.g. when liquid/liquid phase separation precedescrystallisation.

All of these peculiarities make macromolecular crystals very sensitive to the processestransporting growth units from the bulk of the solution towards the crystal face. Thebelief that the convection-free environment provided by microgravity would enhancethe perfection and size of macromolecular crystals triggered the interest of molecularbiologists and structural crystallographers in the use of space facilities. Most of thesespace experiments were performed by direct extrapolation of the on-groundcrystallisation techniques, using blind facilities. Therefore, in most cases the study wasapproached as a ‘black box’ problem, where only the initial conditions and the resultswere known, whilst the actual course of the experiment was unknown.

After fifteen years of conducting experiments in microgravity, improvements in crystalquality and crystal size have been reported in a number of cases. In general, however,the space-grown crystals, evaluated by Wilson-type plots or by mosaicitymeasurements, do not show a dramatic increase of order in the three-dimensionalarrangement of the molecules. More specifically, although it seems clear that thedegree of order is generally higher at low-to-medium resolution, in only a few cases

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2.3.1.3 Required Quality of the Microgravity Environment

In the preceding discussion, two simplifying assumptions have been made. Firstly,that the disturbances to the microgravity environment in an orbiting spacecraft, fromremnant or perturbing accelerations, are of negligible effect. Secondly, that allconvective motions are absent.

In practice, fluid/gas interfaces exist in some protein crystal-growth techniques, namelyin all variations of vapour-transport methods, which are the most commonly usedprotein-crystallisation techniques for on-ground experiments. In that situation, surface-tension-driven Marangoni convection is known to occur (see Section 2.3.4). Obviously,therefore, crystallisation techniques without free liquid surfaces, such as free-interfacediffusion or dialysis, are the appropriate candidates for growing crystals in space. Hence,the discussion about the required quality of the microgravity environment should berestricted to this type of crystallisation technique in which Marangoni convection cannotoccur. However, it is still necessary to consider the possibility that some buoyancy-drivenconvection could occur in response to remnant or induced accelerations, sinceconcentration (density) gradients obviously do exist in the crystallising solutions as anintrinsic consequence of the crystal-growth process itself.

As discussed in Section 1.2, all microgravity experimentation facilities suffer somedegree of residual acceleration and impulse-like ‘g-jitter’, mostly stemming fromOrbiter manoeuvres. It is also known that these g-jitters, particularly those of very lowfrequency, are able to trigger particle motion in solutions. In fact, monitoredexperiments performed by ESA have demonstrated the existence of protein-crystalmotion during Shuttle flights. It is important to emphasise that, in all of these cases,the effect was observed inside interface-free diffusion devices. The relevance of thesemotions in perturbing CDZ symmetry was theoretically analysed and the problemfaced experimentally in two recent ad-hoc experiments performed on the STS-95mission. These experiments were performed in ESA’s Advanced Protein CrystallisationFacility (APCF).

The top row of Figure 2.3.1.1 shows three consecutive interferograms, correspondingto the growth of ferritin crystals. The small crystal in the lower part of the image isattached to the wall of the reactor, while the largest crystal in the centre is floating inthe solution and moves across the field of view (5 mm x 4 mm). The average rate ofmotion of the crystal between the first and second images was R12 = 104 µm/h andbetween the second and third images R23 = 256 µm/h. These relatively fast crystalmovements were induced by large g-jitters during the flight. The bottom row of thefigure shows the concentration fields, reconstructed from the interferogram. Note thatthe depletion zone around the large crystal changes from being slightly deformed inthe left interferogram to being severely distorted in the middle. In the right one, it isalmost non-existent. As expected, whenever the velocity of flow of macromolecules


From this simple analysis it is clear that the existence of a diffusion-controlled mass-transport scenario does not necessarily imply diffusion control of the overall crystalgrowth process. In fact, the experimental βstep data, which are available for severalprotein molecules, together with values found for their diffusion coefficient in water,lead to the conclusion that those protein crystals grow in the so-called ‘mixedtransport-kinetics’ regime under microgravity conditions.

There are two implications arising from this conclusion. Firstly, during the growth ofthe crystal there can be a transition from surface control to mass-transport control, asthe diffusion length increases with the size of the crystal. In that case, the periphery ofthe crystal may have a better quality than its core, and therefore X-ray diffraction datasets from the outer regions of large crystals may provide better structural information.

The second important implication of these results is that the control of the overallcrystal-growth process is very sensitive to the diffusion coefficient of themacromolecule. This is because any increment due, for example, to a convectivecontribution will displace the system towards surface-kinetics control. It is alsorelevant to the recent finding that, due to the coupling between the transport andsurface-kinetic processes, the growth rate of protein crystals fluctuates, even understeady external conditions. It has been proposed that these fluctuations affect thequality of crystals grown in the mixed transport-kinetics regime, as they can bedamped by pushing the system into either transport or surface-kinetics control.

The problem of impurity incorporation into the protein crystal is another importantsubject that is linked to the above discussion. It is known that impurities affect thecrystallisability of nucleic acids. Incorporation of impurities is the source ofmacroscopic disorder observed in protein crystals, as they may increase the latticestrain. The strain can be released by continuous bending of the lattice, bymisalignment of growth-sector boundaries, by formation of mosaic blocks, and bydislocations. It has recently been found that protein crystals grown in space containseveral times less impurities than their terrestrial counterparts. It was also shown thatthe effect of impurities on nucleation and crystal growth is less important in crystalsgrown from gelled solutions than from pure protein solutions. The observed beneficialeffect of such stagnant solutions can be explained by the existence of an impuritydepletion zone, which forms when the crystal preferentially incorporates theimpurities, i.e. when the partition coefficient is larger than unity. The efficiency of thisself-purification process by diffusive ‘filtering’ increases with the volume of the proteinsolution. Certainly, the above discussion only applies if the spherical symmetry of theconcentration depletion zone (either that of the impurity or that of the macromoleculeitself) is ensured. Thus the quality of the microgravity scenario, which will be reviewedin the next section, becomes a critical issue for macromolecular crystallisation.

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These experiments clearly show, for the first time, that the ‘gravitationally’ noisyenvironment on board the Shuttle may provoke not only crystal motion, but alsobuoyancy-driven fluid motion inside interface-free diffusion reactors. They alsodemonstrate that, in some cases, the symmetry of the depletion zone from whichmicrogravity experiments should benefit can actually be broken.

These results have important implications. For example, suppose that the ferritincrystals shown in Figure 2.3.1.1 were grown in a ‘blind’ space experiment and thentheir X-ray quality compared with that of crystals grown on the ground. Should oneconclude that there is any reasonable correlation between ‘microgravity’ and crystalquality? The answer is obviously no, and it implies that better knowledge of thecorrect space environment for crystal growth is presently needed. Monitoring spacecrystallisation experiments with appropriate tools is the only way to obtain usefulinformation for rationalising protein crystallisation. It is also important to obtaininsight into the growth processes occurring close to the crystal face which, because ofthe effect of gravity in terrestrial experiments, are one of the less understood problemsin crystal growth.

2.3.1.4 New Crystallisation Techniques Exploiting Diffusion-Controlled MassTransport

All of the crystallisation techniques currently used on the ground can be implementedunder microgravity conditions. A diverse range of facilities are currently offered byseveral space agencies for growing protein single crystals under microgravityconditions. The so-called ‘hanging (or sitting) drop method’ is an elegant evaporationtechnique developed for protein crystallisation and the most appreciated by molecularbiologists. For that reason, it has been the method most commonly used so far inspace experiments. Unfortunately, for the reasons explained above (the existence of afree fluid interface and the low mechanical stability), an evaporation method is not anappropriate choice for space crystallisation. Interface-free diffusion and dialysismethods have also been tried several times in space. The problem is that the veryexistence of mass transport controlled by diffusion converted most of theseexperiments into a slow mixing batch method, since the time required forequilibration is shorter that the waiting time for nucleation. Finally, space facilities forperforming crystallisation by changing the temperature of the solution have recentlybeen implemented.

Very little has been done to design and explore crystallisation methods that actuallyexploit the potentially convection-less scenario provided by microgravity conditions.One such attempt is the use of a non-equilibrium counter-diffusion technique, whichconsists of the counter-diffusion of the macromolecules and the molecules of theirprecipitating agent, in a two- (or three-) chamber linear device. Thus, both interactingsolutions are placed in line, separated either by a membrane or an intermediate


towards the crystal face is slower than therate of motion of the crystals, thespherical symmetry of the CDZ is broken.

The second experiment was technicallyvery demanding. The objective was toobserve the depletion zone around onlyone fixed single crystal. This was madepossible by gluing a reinforced tetragonallysozyme crystal to the wall of the reactorand then selecting the initial conditions topermit the growth of the crystal whilstavoiding nucleation, i.e. to maintain thesystem inside the metastable zone.

Figure 2.3.1.2 shows the concentrationfield reconstructed from the interfero-gram, demonstrating for the first time theexistence of the depletion zone around agrowing protein crystal in space. Thepicture also shows that the depletionzone, ideally having spherical symmetry,is distorted. This is a consequence of thebuoyancy-driven convection that istriggered by the residual accelerationsand g-jitters.

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Figure 2.3.1.1. Three interferometric images of a ferritin crystal growing in space (STS-95mission). The large crystal floating in the solution is growing within its concentrationdepletion zone (left). Motion of the crystal at a velocity greater than 200 µm/h provokesbreakage of the symmetry of the depletion layer (centre and right pictures obtained about7 h and 14 h later, resp.) The observational window is 5 mm x 4 mm

Figure 2.3.1.2. Interferogram (top) andcorresponding protein concentrationmap showing the concentrationdepletion zone around a protein singlecrystal growing in space (STS-95 mission),glued to the wall of the reactor. Sphericalsymmetry of the depletion zone is lostdue to fluid motion provoked by g-jitter

those used in classical ‘drop’ techniques. In fact, an apparatus that exploits thecounter-diffusion technique by using X-ray capillaries as the protein chamber, theGranada Crystallisation Box, will soon be commercially available. In addition to theadvantage of reducing the number of trials in the screening for optimal crystallisationconditions, this apparatus also avoids post-crystallisation manipulation of crystals forX-ray diffraction.

2.3.1.5 Simulating Microgravity

As already mentioned, all the expected benefits of space crystallisation come from theability of the microgravity scenario to reduce density-driven convection. It includes thepossibility to grow the crystals under diffusion control, to homogenise and reduceimpurity concentrations at the crystal face, and to avoid sedimentation of crystals aswell as the secondary nucleation of 3D protein clusters. To identify the environmentsable to reduce convective fluid motion, it is convenient to use the dimensionlessGrashof number (GrN), which accounts for the relative importance of buoyancy andviscous forces in a fluid system.


chamber containing either a free fluid or a chemically inert gel. The very nature of thetechnique requires a diffusive environment, because convection will destroy thesymmetry of the precipitation pattern.

The initial conditions are selected to provoke the precipitation of the protein far fromequilibrium – at very high supersaturation – as soon as the precipitating agent meetsthe protein solution. Because the molecules of the precipitating agent (usually either asalt or polyethylene glycol) diffuse faster than the biological macromolecules (typicallyone to two orders of magnitude faster), the precipitation phenomena occur in theprotein chamber. Due to the coupling between mass transport and precipitation, awave of supersaturation is triggered which moves across the protein chamber withdecreasing amplitude. This provokes successive precipitation phenomena, occurringunder different crystallisation conditions, namely at decreasing supersaturationvalues.

The advantages of the technique over classical crystallisation techniques are thatwhile vapour diffusion or batch methods scan only one crystallisation condition perexperiment, this counter-diffusion technique explores a large range of crystallisationconditions in one single experiment. The technique was tested under microgravityusing an ad-hoc designed APCF reactor with a long protein chamber, a sine qua noncondition for permitting spatial development of the precipitation pattern. Theexperiment confirmed the existence of such a supersaturation wave, which wasobserved for the first time.

As shown in Figure 2.3.1.3, the maximum of supersaturation advances as a wave, itsamplitude decreasing and its width increasing as the wave moves across the proteinchamber with decreasing velocity. As the supersaturation wave moves towardsequilibrium, it automatically screens for the best growth conditions. In fact, thecrystals obtained by this automatic screening produced the highest-quality X-ray-diffraction data ever collected (completeness of 98.4% in the 0.94–25 Å resolutionshell) from crystals of the model protein in the experiment (tetragonal hen-egg-whitelysozyme). Because of the g-jitters triggered by the release and retrieval of a satelliteduring this Shuttle mission and by the thruster firing system, the dynamics of thesupersaturation wave were affected on three different occasions. This demonstratesonce again that ‘gravitational’ noise due to stray accelerations may affect thecrystallisation process, this time at the scale of the whole reactor.

An early criticism of space crystallisation was that the limited number of opportunitiesfor flying experiments makes it impossible to employ the trial and error methodologyused so far on Earth in the search for optimum crystallisation conditions. It is evidentthat this type of counter-diffusion experiment provides an interesting opportunity forthose who wish to use that methodology, particularly as the use of capillaries asgrowth chambers reduces the volume of protein needed to values comparable to

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Figure 2.3.1.3. Development of supersaturation across a 70 mm-long protein chamber in anon-equilibrium counter-diffusion experiment performed in space (on the STS-95 Shuttlemission). The data correspond to the actual development in time and space of thesupersaturation values obtained by interferometric analysis. The precipitating agentdiffuses from left to right, creating a wave of supersaturation that moves across the proteinchamber. It provokes successive protein-crystallisation events under increasinglyfavourable conditions for optimal crystal quality. Despite three perturbations of the trendprovoked by g-jitters, the best crystals (0.94 Å resolution) of the model protein tetragonalHEW lysozyme ever grown were obtained in this experiment

Another way to reduce L is to gel the macromolecular solution. The pore size of the gel(which now defines the characteristic length of the system L) is usually a function ofthe polymer concentration used for gelling purposes. A typical pore-size distributionis on the scale of nanometres, thus making gels an excellent crystallisation scenarioable to remove buoyancy and sedimentation. The gelling of the ‘mother solution’ is atechnique that has been used in crystallisation experiments for many years.Obviously, it involves the addition of a foreign chemical (agarose, silica, acrylamide,etc.) to the mother solution, to provoke the polymerisation reaction. These chemicalsare known to either retard or enhance the nucleation of some globular proteins. Thiscreates some difficulties in the use of gelled solutions when fundamental aspects ofthe crystallisation process are being investigated.

It is known that, unlike most inorganic crystals, protein crystals incorporate thepolymer fibres when they grow in gels, although the crystallisation pressure exertedis higher than the gel strength. There are not yet enough data available to assess thefull effect of gel incorporation on crystal quality. However, in the few cases wheremosaicity and resolution limit were measured, an unexpectedly high quality of thediffraction data set and rocking curves was observed. Finally, increasing the viscosityof the system can also reduce GrN. This can be done with the same polymerisationcompounds used for gelling purposes. For instance, agarose at a concentration lowerthan the critical concentration to form a gel produces a non-Newtonian viscous fluidable to avoid sedimentation and buoyancy, thus reducing the risk of chemicalinteraction with macromolecules.

2.3.1.6 Conclusions

It seems advisable to maintain the current ESA strategy for understandingmacromolecular crystallisation, combining terrestrial research with monitored spaceexperiments. In the past, this was possible due to the design of the APCF, consideredone of the outstanding space-crystallisation facilities with almost zero risk ofmalfunction. During the past five years, this strategy has yielded the valuablefundamental knowledge reviewed above. In addition, it has provided the basis for thedesign of a new diagnostic machine, the Protein Crystallisation Diagnostic Facility(PCDF), which is the best machine available today for simultaneous characterisationby different techniques of protein nucleation and growth, either for space or forground experimentation. The PCDF, which can be considered a spin-off of the ESAMicrogravity Research Programme, includes several characterisation techniques.These include phase-shifting Mach-Zehnder interferometry, dynamic light scattering,low- and high-resolution microscopy, and thermal control, and it allows differentcrystallisation techniques to be used. It will permit the study of some critical but notyet fully understood crystallisation problems, such as the nature of crystallisingsolutions and the nucleation process.


GrN = L3.α.∆c.g.ν-2

where L is the thickness of the reactor (cm), ∆c is the concentration difference, ALPHAis the solutal expansivity in cm3/mg (the ratio of change in density to change inconcentration), and ν is the kinematic viscosity (cm2/s-1). Note that to reduce Gr,either the value of g can be reduced, or the characteristic length of the reactor reduced,or the viscosity of the fluid increased. It is also possible to tune the density gradient,but the effect is not dramatic and moreover this is difficult to implement in

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Figure 2.3.1.4. Variation in dimensionless (mass) Grashof number with the characteristiclength of the reactor, for three different values of gravity. The minimum practical crystal sizefor X-ray studies refers to most conventional X-ray sources

crystallisation techniques. Figure 2.3.1.4 shows the variation in GrN as a function of L,for three values of g, using data relevant to protein crystallisation.

Reducing the dimensions of the reactor by using capillaries is very effective, becauseL appears to the third power in the Grashof number. Batch crystallisation insidecapillary volumes has been used to illustrate diffusive transport in proteincrystallisation. As pointed out above, the non-equilibrium counter-diffusion techniquewas implemented using X-ray capillaries as a protein chamber. Using an innovativeimplementation that basically consists of punching the capillary into a gel of agaroseor silica, the counter-diffusion technique can be used on the ground. However, it is nowknown that X-ray capillaries are not able to completely remove buoyancy-drivenconvection when used under terrestrial conditions. A negligible contribution frombuoyancy-driven forces can be expected only for diameters of less than 1 µm, i.e.much smaller than the minimum size of crystals useful for X-ray diffractionexperiments. As can be seen from Figure 2.3.1.4, a combination of X-ray capillariesand microgravity (even milligravity) seems very promising.

Ducruix A. & Giege R. 1999, Methods of Crystallisation. In: Crystallisation of NucleicAcids and Proteins: A Practical Approach (Eds. A. Ducruix & R. Giegé), IRL Press, Oxford,pp. 121–148.

McPherson A. 1999, Crystallisation of Biological Macromolecules, Cold Spring HarborLaboratory Press, 300 pp.

Robert M.C., Vidal O., García-Ruiz J.M. & Otálora F. 1999, Crystallisation in gels andrelated methods. In: Crystallisation of Nucleic Acids and Proteins: A Practical Approach(Eds. A. Ducruix & R. Giegé), IRL Press, Oxford, pp. 149–176.

Walter H.U. (Ed.) 1987, Fluid Sciences and Materials Sciences in Space, Springer Verlag.


Concerning applications, the main target for macromolecular crystallisation is thegrowth of crystals of superior quality for X-ray structural determination. Mostmolecular biologists like to use the trial-and-error methodology to meet that target. Inspace experimentation, such a methodology is not compatible with monitoredexperiments. It is therefore advisable to design inexpensive devices optimising thenumber of experiments by volume and weight. The Granada Crystallisation Box (GCB)is one example. This very inexpensive passive crystallisation box combines gels andX-ray capillaries and allows more than 600 counter-diffusion experiments to beconducted within one cubic decimetre. These applied experiments should beperformed with macromolecules already crystallised on the ground, but it is difficultto do so at high resolution (less than 2 Å). In any case, the selection process forreactors and crystallisation techniques for blind experiments must take into accountthe features of the space scenario discussed above.

The prospects for future commercial applications of macromolecular crystallisation inspace certainly depend upon having the skill to develop imaginative tools forobtaining high-quality crystals. In addition, however, they also depend on externalfactors such as the availability of universal gels or high-viscosity fluids that do notinterfere with the crystal quality, and on improvements in synchrotron X-ray sources.

Finally, it can be expected that the crystallisation of biological macromolecules will, inthe future, face the challenge of growing the larger crystals for purposes such asneutron diffraction measurements. In fact, the interest in large macromolecularcrystals will lie also in characterisation studies of their physical properties, becausetheir technological application is still an unexplored and exciting field. Microgravityoffers an appropriate environment to grow these large macromolecular single crystals.It can avoid the limitations inherent in the use of capillary volumes. First, however, itis necessary to control impurity distribution and its effects on the cessation of growth.

Acknowledgements

We acknowledge the useful suggestions of our colleagues in the ESA Topical Team on‘Fundamental Aspects of Macromolecular Crystallisation under Microgravity’.

Further Reading

Chernov A.A. 1984, Modern Crystallography III: Crystal Growth, Springer Verlag, 517 p.

Drenth J. 1999, Principles of X-ray Crystallography, Springer.

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influence the growth process and govern the crystallographic perfection of the growncrystal, as well as the concentration and distribution of defects and of dopingelements. Crystal growth under reduced gravity in space reduces buoyancyconvection drastically. Heat and mass transport may then be dominated by diffusionand it has been demonstrated theoretically that this happens when the magnitude ofthe buoyancy convective flow is reduced below the microscopic growth velocity.

However, in the presence of fluctuations in the residual gravity field, which alwaysexist on space-transportation vehicles, this condition cannot be guaranteed and itrequires specific attention. More generally, the application of external forces on themelt, such as static or transient magnetic or electric fields, provides the opportunityto study the growth under a number of flow configurations that are difficult to achieveon the Earth, because of the masking effect of the buoyancy convection.

There is another type of convection that is independent of gravity, which can occur inliquids (melts) that present a free surface to a gas or another liquid. The surface tensionat the free surface decreases with increasing temperature. Hence if there is anytemperature gradient parallel to the surface, a stress gradient may develop from hotto cold, resulting in a gravity-independent convection. This is the Marangoniconvection, discussed in Section 2.3.4, and illustrated in Figure 2.3.2.1b. The influenceof this additional convection process on the crystal growth can be studied only undermicrogravity conditions. Otherwise, its effects are masked by normal convection.

Gravity also causes hydrostatic pressure in melts and this in turn influences the shapeof a liquid surface. Under microgravity conditions, the liquid shape is only determinedby the surface tension. The shape of floating liquid zones is therefore likely to bemodified in the absence of gravity. Also, the wetting behaviour of the melt on solidsurfaces, such as seeds, crucibles or technical parts is modified by the absence ofgravity, and liquid meniscii are formed that markedly influence the crystal-growthprocess.


2.3.2 Crystal Growth of Inorganic Materials

K.W. Benz, T. Duffar & M. Fiederle


Single crystals consist of three-dimensional, regular arrangements of atoms, ions, ormolecules. Their industrial use has grown rapidly in recent decades and continues toincrease. Single crystals of silicon, for example, are the very basis of the ‘electronicage’. Modern computers would not be possible without the ready availability ofintegrated circuits made on wafers of single-crystal silicon.

Semiconductors such as silicon cannot be found as minerals in nature. They first haveto be produced as an extremely pure chemical, and then grown as a single crystal,under conditions that ensure a very high level of chemical purity, homogeneity andcrystalline perfection. Single crystals may be grown either from the melt, from asolution, or from a vapour phase via a solidification process. In the so-called‘Czochralski process’, which is widely used in the semiconductor industry, a smallsingle crystal (seed) is first dipped into the molten material. It is then very slowlywithdrawn. In so doing, the original small seed crystal begins to grow, increasing inboth diameter and length simultaneously. Some 10 000 tons of silicon single crystalsare produced each year by such methods.

Unfortunately, crystals do not grow readily in the ideal geometrical arrangement oftheir atoms. A crystal will normally contain growth defects such as vacancies orinterstitials, where atoms have wrongly been omitted or added. There will bedislocations in the regular layers of atoms, extraneous grain boundaries, or inclusionsof impurities. For technical applications such as computer chips with an increasingdevice density, the quality of these semiconductor crystals, expressed in terms of lowdefect density and crystallographic perfection, must be continuously improved.

The scientific objective of research into crystal growth for such applications is toexplain the connection between the resulting crystal quality, its physical propertiesand the parameters of the growth process. Gravity is found to play a very importantrole in all of the various growth processes, as already discussed in Section 2.3.1.

In general, heat and mass transport in the melt, in the solution or in the vapour phase,are all influenced by convective flows. These are normally created as a result ofbuoyancy effects. In the gravitational field, hot and less dense melt rises and thecolder, denser melt sinks down (Fig. 2.3.2.1a). In turn, heat and mass transport

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Figure 2.3.2.1. (a) Buoyancy convection. (b) Marangoni convection

(a) (b)

core technology underpinning the whole electronics and opto-electronics industry.Single crystals of silicon are the basis of more than 90% of the electronics market. TheIII-V compound semiconductors are basic materials for opto-electronic devices andintegrated circuits with ultra-short switching times (e.g. GaAs).

Unfortunately, some people have attempted to justify space experiments on thesematerials in terms of a potential for commercial crystal growth in space, despite thefact that specialists have argued for over 15 years that this idea is totally unrealisticon both technical and economic grounds. Nonetheless, some still persist with sucharguments.

2.3.2.2 Crystal-growth Experiments over the Past 25 Years

- Studies of Chemical Segregation in Bridgman Crystal Growth

A principal objective of the past space experiments has been to study the origin ofchemical heterogeneities, at the macroscopic (axial and radial segregation) andmicroscopic (striation) level, in connection with fluid dynamics in the melt. Growthexperiments in space with confined melts will have no Marangoni convection and no,or highly reduced, laminar buoyancy convection (depending on the size of the residualgravity vector during the experiments in space). They should therefore exhibit a purelydiffusive nutrient transport process and thus produce homogeneous crystals.

The first space experiments tested this concept of diffusion-limited solidification andthe avoidance of dopant striations. It was shown that, in contrast to Earth-processedsamples, there were no striations visible in doped indium antimonide. That was truealso for doped germanium crystals. The overall distribution of doping elements wasalso found to fit perfectly with what was theoretically expected for the case of purediffusion transport in the melt. These results have been confirmed during a number ofsubsequent space experiments.

Simultaneously, the physical understanding of the coupling between solidification andfluid flow has been improved, and it became possible to take into account the effect ofthe residual gravity in spacecraft on the chemical perfection of the grown crystals.Figure 2.3.2.2 shows two zones, separated by theoretical lines, representing,respectively, growth perturbed by fluid flow and unperturbed growth. All of the resultsof space experiments focusing on this subject are in agreement with this theoreticalprediction (see Garandet & Dufar (1999) for a review on this research topic).

- Results of Floating-Zone Experiments in Mirror Furnaces

Another point of interest was related to the effect of free-surface (Marangoni)convection on crystal growth and the effect of the absence of gravity on the shape of


Consequently, the motivation for carrying out crystal-growth experiments in spaceand the related scientific topics to be explored can be summarised as:– Study of crystal growth under purely diffusive conditions.– Study of the effect of buoyancy convective flows on crystal growth and quality,

mainly chemical heterogeneity, by comparing space- and ground-basedexperiments.

– Investigations of the influence of residual microgravity on homogeneity at themacro- and micro-scale.

– Study of the solute segregations caused by stationary and time-dependentMarangoni flows.

– Effect of such flows on solid/liquid interface shape and velocity.– Reduction of defect concentration and heterogeneity.– Study of the effect of gravity on the size and shape of floating zones.– Establishment of wall-free configurations for the growth, and study of the effect on

crystal quality.– Investigations into the control of transport conditions in melts and solutions by the

application of external fields, such as rotating or stationary magnetic fields.

An overview is presented below of the crystal-growth experiments performed inmicrogravity over the past 25 years.

- Selection of Materials

So far, about one hundred experiments focusing on inorganic crystal growth havebeen performed in space. Scientists from the former Soviet Union have grown a largeamount of crystals onboard the Salyut and Mir space stations. Unfortunately, data onthese experiments and their results are very scarce and only those that are welldocumented are included in this discussion. Ninety percent of those experiments werededicated to semiconductor materials for the following reasons:– Their potential application in industry has prompted worldwide experimental and

theoretical studies of their physical and chemical properties and of their growthprocess, so that they are particularly well-known materials.

– Potentially, growth under microgravity conditions can give perfectly homogeneouscrystals, which are of considerable interest for applications.

– Many characterisation techniques have been developed in the past and areavailable to study the crystals on a broad, reliable and sensitive basis.

– The expensive Space Shuttle programme needed an economic justification and thatincluded research on applications-oriented materials.

The selection of materials has therefore focused on semiconductors. It has includedsilicon and germanium (Si and Ge), the III-V compounds, gallium arsenide (GaAs),gallium antimonide (GaSb), and indium phosphide (InP), and also cadmium telluride(CdTe), and mercury cadmium telluride. Crystal growth of these materials belongs to a

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The striation formation in the grown crystal was used as evidence of such flow andallowed the tracking of fluid dynamics within the molten silicon.

The most important results of the floating-zone experiments under reduced gravity, incomparison with 1g reference experiments, are the following: – Dopant striations in floating-zone silicon are caused by time–dependent Marangoni

convection. If the free surface of the molten silicon is covered, e.g. with a silicon-oxide layer, the Marangoni convection is suppressed and with it the striations. Thisimportant effect of Marangoni convection was impossible to demonstrate on Earthbecause of the masking effect of the buoyancy convection, and it was taken ashighly hypothetical until the publication of these space results.

– The transition regime from laminar flow to time-dependent surface convectioncould be evaluated by microgravity and 1g reference experiments. For example,during the Texus-10 campaign, a striation-free crystal was obtained by working with


these surfaces. The restricted space and power availability on board spacecraft led tothe development of well-defined growth facilities such as the mono-ellipsoidal anddouble-ellipsoidal mirror furnaces for the floating-zone growth technique.

Crystal growth by the floating-zone technique involves a single crystalline rod that ispartially melted. The zone to be melted remains fixed between the upper and lowercrystalline parts and is positioned at the lower focus of the mirror furnace (Fig. 2.3.2.3).It is melted by a halogen lamp located at the upper focus. By moving the furnace withrespect to the sample, crystallisation at the advancing melt/seed interface is achieved.Simultaneously, feed material is dissolved at the feed/melt interface. The weight anddiameter of the liquid zone are limited on Earth (diam. less than 10 mm), due to theweight of the molten zone itself which cannot be sustained by surface forces for thelarger diameters. In similar space experiments, there is no such limitation and crystalswith a dramatically increased diameters can be grown. Figure 2.3.2.4 shows freesilicon melt zones on Earth and in space (Texus-29 sounding-rocket experiment). Thezone on Earth is bottle-shaped, due to its weight.

In practice, only silicon is grown on Earth by the floating-zone process, thanks to itslow density. It has been used to study the details of Marangoni-flow during growth.

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Figure 2.3.2.2. This GrSc/Pe diagram can be interpreted as a convection/growth ratediagram. The two straight lines are the theoretical prediction for the transition betweendiffusion-dominated transport in the melt (lower right side, unperturbed crystal growth)and convection-dominated transport (upper left side, chemical homogeneity perturbed byfluid flow). The points correspond to all the experiments performed in space for whichdiffusive (dots) or convective (triangles) transport has been experimentally andunambiguously identified. The MEPHISTO point (see Chapter 4.1.3) corresponds to theexperimental transition obtained by varying the growth rate at constant convective level

Figure 2.3.2.3. Principle ofthe double-ellipsoid mirrorfurnace

- Contact-free Crystal Growth in Crucibles by the Bridgman Method

Directional solidification is the growth technique used most in the industrialsemiconductor business. Conventional semiconductors, like germanium or galliumarsenide, are grown from the melt by the Bridgman or Czochralski method. Someothers, like cadmium telluride, are only grown by the Bridgman process. A commonproblem with the Bridgman method stems from the use of crucibles. The contact withthe crucible produces distortions of the thermal field in the sample and hence stresspatterns in the growing crystal. These stress patterns induce defects, such asdislocations or twin and grain boundaries. The crystallinity is also reduced due tospurious nucleation in the case of crucible contact.

In most of the Bridgman space experiments, it has been observed that the crystal wasdetached from the crucible and that the structure of the crystals grown was improvedcompared to the Earth-grown material. In many cases, large diameter differences werefound. The first observations were made for indium gallium antimonide, InGaSb, onboard Skylab in 1974.

The list of materials in the field of detached experiments ranged from metals like silveror aluminium to many kinds of semiconductors. In all of these experiments, thecrystals were grown partially detached. The observed gaps between crystals andcrucibles were not constant, either in the growth direction or in the radial direction.The growth conditions are unstable and not reproducible. In space there are a numberof configurations that lead to detachment of the crystal from the crucible, includingbubbles, geometrical free-surface generation, and shrinkage.

In contrast, ‘dewetting’ refers to the particular case in which a very thin and regulargap is established between the crystal and the crucible. Consequently, at thesolid/melt interface the crystal is not touching or wetting the crucible wall. Forexample, a gap of 20 ± 2 µm was observed all along the 4 cm of a GaInSb samplegrown during the LMS mission in a boron-nitride crucible. On Earth, the melt wets thecrucible due to the hydrostatic pressure. In microgravity, the hydrostatic pressurevanishes and the melt shape and position depend only upon capillary forces.

This behaviour is dependent on the crucible material and the so-called ‘wetting angle’of the semiconductor melt on it. The important parameters for dewetting are thecrucible material and preparation, the vapour pressure in the closed crucible, and thewetting parameters of the crystal melt. In some cases, as shown on Figure 2.3.2.6, asimple geometric consideration between the wetting and growing angles leads todewetting. In some other cases, it is necessary to take into account the gas pressurethat is acting on the melt surfaces and some pollution of those surfaces. This is thereason why dewetting is not yet a fully understood and reproducible phenomenon.


a small sample of gallium-dopedgermanium in a low temperaturegradient (without coating the m e l tsurface).

– The additional laminar convection on Earth affects both the axial and theradial macro-segregation in dopedsilicon crystals, which could bedemonstrated by resistivitymeasurements.

Other growth experiments using thefloating-zone technique in space werededicated to compound semiconductorssuch as gallium arsenide and galliumantimonide. The objective in this casewas to produce commercially importantmaterials in sizes not attainable on Earthwith the same technique. GaAs crystalsof 20 mm diameter were grown duringthe Spacelab-D2 mission (the maximumdiameter achieved with this method on

Earth is 6 mm). The crystals contained dopant striations, as expected, due to thepresence of Marangoni convection in the uncoated GaAs melt. Floating-zone growthof gallium-antimonide crystals was performed during the Spacehab-4 mission. Figure2.3.2.5 shows the samples prepared for the space experiments, as well as two 16 mm-diameter space-grown crystals compared with the size of the Earth-grown crystal.

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Figure 2.3.2.4. A floating-zone experiment with silicon: microgravity and 1g referenceexperiment (Texus-29)

Figure 2.3.2.5. Gallium-antimonide (GaSb)crystals grown during the Spacehab-4 (STS-77) mission in May/June 1996


Dewetting is generally associated with adecrease in structural defect density in thecrystals. For example, investigations of thequenching and back melting of pre-processed crystals have been studied forthe HgTe–ZnTe system. The density ofdefects (e.g. subgrain boundaries) wasfound to be reduced after this spacetreatment. To improve their structuralquality, CdTe and (Cd,Zn)Te crystals weregrown under microgravity to study themechanism and effect of dewettinggrowth. Encouraging results were obtainedfrom the USML-1 and -2 missions. It wasshown that the etch pitch (i.e. dislocation)density was reduced by a factor of 400compared to the Earth-grown sample. Thisimprovement was correlated with thedewetting-grown part of the crystal. Ascientific review on this topic can be foundin Regel & Wilcox (1998).

The discovery of the dewetting phenomenon in space and the understanding of itsphysical basis has led to the development of a ground-based process. In this, thedewetting is obtained by counterbalancing the hydrostatic pressure with an inert gasacting on the fluid. This has permitted a considerable enhancement of crystallinity inthe case of GaSb. The process is under development for more useful crystals such ascadmium telluride, which could not previously be obtained on Earth as a single crystalbecause of the crystal-crucible sticking phenomenon.

- Solution Growth: The Travelling-Heater Method and Rotating Magnetic Field

Growth from a solution can be used to grow semiconductors as well as organic orinorganic materials. It offers the possibility of growing nearly perfect single crystals,due to a lower growth temperature compared with growth from the melt. Defect andheterogeneity formation is significantly reduced.

Using, as solvent, alkaline water at high pressure (hydrothermal growth) or moltensalts or oxides (flux growth), this process is very important in the industrial productionof oxide crystals such as piezo-electric quartz or magnetic garnets.

Several experiments have been performed in microgravity to grow single crystals frommetallic solutions for various semiconductors, including germanium, gallium arsenide

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Figure 2.3.2.6. Parameters of thedewetting phenomenon are the growingangle, α, that always exists between afree melt and its solid phase and thewetting angle, θ, of the melt on thecrucible

and ternary compounds. During the Spacelab-D1 mission, GaSb and InP were grownby the Travelling-Heater Method (THM). This is a very powerful method for growingsingle crystals with the same level of perfection as the epitaxial layers grown by Liquid-Phase Epitaxy (LPE). Both techniques are very similar, but THM uses a temperaturegradient perpendicular to the growing interface and the growth temperature issignificantly higher than for LPE. This offers the advantage of a higher growth rate andit permits the growth of bulk single crystals when feed material is used.

The objective of the THM experiments that were carried out in microgravity was togrow bulk single crystals in order to study the origins of dopant or compositionalheterogeneities (striations) and defects. Under normal gravity, two kinds of striationsare present: Type-I striations are induced by time-dependent buoyancy flows in thesolution, while Type-II, or kinetic, striations are closely related to morphologicalinstabilities in the growth face and are therefore gravity-independent. Withoutdisturbances from the time-dependent flows, which are absent in microgravity, it hasbeen possible to measure and calculate the critical growth velocity that is responsiblefor the formation of Type-II striations. Below this growth velocity, they disappeared. Atechnique was established and patented that avoids the formation of Type-II striations.It can be used for the growth of semiconductors by THM or LPE, as well as for thegrowth of oxide crystals from solutions.

The use of external fields, e.g. magnetic fields, is of important interest for bothscientific and industrial crystal-growth processes. It provides the possibility to controlthe flow in the solution and to improve material homogeneity in terms of structuraldefects and dopants. A constant magnetic field produces an induced Lorentz force,which acts as a damping force on the moving fluid. The mixing of the material andthus the homogeneity are both reduced. If, however, a rotating magnetic field is used,it induces a current and the resulting force generates a forced convection. The mixingis then increased and a homogenous distribution is obtained.

Experiments were carried out for different materials, under transport regimes drivenby diffusion (under microgravity), 1g convection or forced convection. THMexperiments for CdTe, Cd(Se,Te) and (Cd,Zn)Te were performed on three Russianmissions (Foton-7 to -9) in the Zona-4 facility. In all three configurations, a rotatingmagnetic field was applied to the tellurium solution zone. The results demonstratedthe improved homogeneity that it provided.

Figure 2.3.2.7 shows a CdTe crystal. It is an infrared image of a 2 mm axial crystal slicedivided into five parts: (a) seed crystal (b) grown crystal within magnetic field (c) growncrystal without magnetic field, (d) Te zone and (e) feed material. Between (b) and (c), thenumber of Te inclusions (black spots) is significantly increased. This is correlated withthe effect of the rotating magnetic field and the improved mixing in the (b) part. Thepositive effect for the homogeneity of transport properties could also be determined.

In Figure 2.3.2.8, the product of lifetime and mobility is presented as a function ofcrystal position. In the part grown within the magnetic field, the values are nearlyconstant.

- Growth from the Vapour Phase

From the point of view of lowest growth temperature and best equilibrium conditions,growth from the vapour phase is the most attractive of all of the methods. Forindustrial processing, the limitations are set by the low growth rate and the smalldiameter of the crystals. Gaseous impurities affect the mass flow disadvantageously –especially in closed systems. Furthermore, the crystal’s compositional perfection isdisturbed by gravity-induced convection instabilities in the vapour. Growthexperiments have to be performed under well-defined conditions in order to optimisegrowth rates and crystal quality.

Mercuric iodide (HgI2) was the typical model substance for growth experiments fromthe vapour phase under microgravity, using the Physical Vapour Transport method.This essentially involves evaporation from the hot side of a cell and deposition at the


Figure 2.3.2.8. The mobility-lifetime product as a function of crystal length (with andwithout an applied rotating magnetic field) for a cadmium-telluride crystal, grown by theTravelling-Heater Method in a rotating magnetic field on the Foton-7 mission

Figure 2.3.2.7. An infrared image of a 2 mm axial slice of cadmium-telluride crystal

In the future, space crystal-growth experiment activities will inevitably beconcentrated on the International Space Station (ISS). As the residual gravity level inthe ISS will be rather high, there will be an additional need for some experiments onShuttle missions or satellites and sounding rockets. But the possibility of more andlonger-term growth experiments, newly defined conditions and reproducible resultswill only be realisable on the International Space Station. The key topics in the field ofcrystal growth are likely to be:– Wall-free growth of semiconductors from the melt: dewetting growth of CdTe and

related compounds of Si and Ge.– Growth from the vapour phase: identification of growth limits (growth rate and size

of crystals), and the scaling-up of scientific configurations for industrial needs.– Further studies on chemical segregation in crystal growth, in the field of radial

segregation and striations, and in the case of highly concentrated alloys.

Taking advantage of the previous results, the new generation of space facilities aredesigned with in-situ diagnostic capabilities to measure real-time experimental dataand to process materials at higher temperatures. This will provide us with even deeperknowledge of the gravity-related physical phenomena that affect crystal-growthprocesses.

Further Reading

Garandet J.P. & Duffar T. (in press), Physics of Fluids in Microgravity (Ed. R. Monti),Chapter 13, Gordon and Breach (Review article with 201 References).

Regel L.L. & Wilcox W.R. 1998, Microgravity Science and Technology, Vol. XI/4, p. 152(Review article with 157 References).

Walter H.U. (Ed.) 1987, Fluid Sciences and Materials Science in Space, Springer Verlag(Chapters X, XI, XII and XIII deal, respectively, with crystal growth from the melt, fromthe vapour phase, and from solutions of biological materials).


cold side. Important results included the following findings:– Growth rates depended upon growth direction and surface-kinetics effects.– Gravity affected the mass-density-gradient layer that is present all around the

growing crystal, much more than the overall vapour flow.– Surface roughness and rocking curves showed better crystalline quality of all space-

grown samples.

In the other vapour-growth method, known as ‘Chemical Vapour Transport’, achemical reactant is used to transport the material from a feed zone, at hightemperature, to the growth zone, at a rather lower temperature. The quality and sizeof the crystals obtained by this technique in space were generally better than forEarth-grown crystals, and measured growth rates were within the error limits oftheoretical predictions for diffusive mass transfer. For example, iodine was also usedfor the transport of Ge and diffusive mass transfer was clearly in evidence, allowingcomputation of the kinetic factors of the heterogeneous reaction governing thevapour-phase transport.

2.3.2.3 Conclusion and Future Activities

The main reason for performing crystal-growth experiments in space is to understandthe role of the basic transport mechanisms in determining the final properties of thecrystals grown. This in turn may help to improve the crystal quality of technicallyinteresting and valuable materials back on Earth. Detailed studies are planned of thecoupling between the many parameters controlling the growth process. This finecontrol of process-related parameters, including (micro)gravity, has the potential tobring major economic benefits. For example, the semiconductor laser was invented in1962. An economic industrial breakthrough was only finally reached some 20 yearslater, after improvements to the crystal-growth process for laser-device fabrication.

An improved understanding of crystal-growth processes, gained from previousexperiments performed in microgravity, has permitted the development of newtechnologies on the ground. This includes the use of magnetic fields or baffles, in orderto decrease the convective flow level in Bridgman, Czochralski and floating-zonetechniques. The use of molten encapsulants or of gas pressure differences, in order tocounterbalance the hydrostatic pressure and so avoid crystal/crucible contact, hasallowed the achievement of dewetting conditions also on Earth, and consequently hasprovided improved crystals. Better knowledge of the effects of Marangoni convectionhas permitted improvements in the silicon-crystal production process.

From the first encouraging results, it was thought that a truly industrial crystal-growthproduction process in space would be very valuable. However, further results haveshown that, due to size, energy, time and above all unavoidable residual gravityfluctuations, this cannot be expected in the near-term.

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this effect in a foundry casting of a several-ton ingot with, on the left, the distributionof the two basic microstructures: (i) columnar dendrites, grown in an array from themould wall inwards (see also Fig. 2.3.3.6), and (ii) equiaxed grains, packed together inthe centre. Depending on their local proximity to thermodynamic equilibrium, thesechange from globular at the bottom to dendritic (tree-like, with branches in cascade)at the top.

The mechanical properties of these materials such as strength, creep and wearresistance and ductility, as well as their chemical, magnetic and electroniccharacteristics, are determined by the structure, chemical composition and numberand kind of defects produced, at all length scales, during the material synthesisprocess. Besides the atomic scale, inherent to condensed matter, and the intermediatescales associated with the solidification microstructures, fluid flow driven by gravitygenerally occurs in the melt at the macroscopic scale of the cast product.Consequently, the relevant length scales in casting are spread over 10 orders ofmagnitude. They range from the atomic size (capillary length, crystalline defects suchas dislocations, attachment of atoms, etc.) to the metre size of the ingot (fluid flow),going through the micron (spacing of dendrite side branches) and the millimetre levels(columnar microstructure, solute diffusion). It follows, therefore, that for high-precisioncastings, the control of material structure during the liquid-to-solid phase transition isabsolutely crucial in terms of quality control and for the design of advanced materialsfor specific technological applications.


2.3.3. Microstructure and Control in Advanced Casting Processes

B. Billia & H.-J. Fecht


Cast materials are common objects in everyday life, primarily because of their goodmechanical properties, resulting from their ability to sustain and/or transmit forceswith negligible damage. The production and fabrication of such materials by thecasting and foundry industry generates a considerable amount of wealth withinEurope. Some 10 million tons of castings were produced within the European Union in1993, worth around 18 billion Euros. The continuation of this business in Europe reliesupon maintaining and improving the industry’s competitiveness with the UnitedStates, Japan and others, in the design and processing of structural materials.Competition is severe and therefore there has to be a continuing effort in Europe toproduce materials of higher performance, to optimise their characteristics for specificapplications, and to improve processing controls.

Casting is a non-equilibrium process inwhich a molten alloy is solidified. Theliquid–solid transition is driven by thedeparture from thermodynamicequilibrium, in the same way thatcooling pure water below 0°C results inthe formation of ice. From the standpointof physics, casting thus belongs to thevast realm of out-of-equilibriumprocesses in which unwanted patternsmay form. Rather than growing evenly inspace and smoothly in time, the solidphase prefers to form a diversity ofmicrostructures. Figure 2.3.3.1 shows

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Figure 2.3.3.1. Schematic of a longitudinal cut in aheavy steel ingot. The distribution of the differentmicrostructures is shown on the left, and that ofthe carbon concentration on the right (negativecarbon segregation, due to sedimentation ofequiaxed crystals, can be seen at the bottom, andpositive segregation on top) (from T. Mazet, PhD Thesis, Institut National Polytechnique deLorraine, 1995)

Figure 2.3.3.2. Filling simulation and temperature distribution for a car engine-blockproduced using Magmasoft® software

It is in these contexts that experimentation in the microgravity environment hasrepeatedly proved of value. Indeed, beyond the inherent technological processdifficulties that need to be overcome in a gravity environment, particularly when hightemperatures are involved, there are at least two major limiting factors on Earth. Thefirst is the contribution to transport in the melt by gravity-induced fluid flow, whichcarries away heat and chemical species and adds to the step-by-step diffusivetransport by means of atomic or molecular displacements. This effect is responsible,for example, for the very large uncertainties in the measurement of diffusioncoefficients, as well as for the drastic changes in the size and/or type of solidificationmicrostructure and strong macro-segregation of components that may render castmaterials unusable. The second effect is due directly to gravity, resulting in theproblem of holding and positioning during containerless processing, and also leadingto sedimentation effects and lack of homogeneity in mixtures and dispersions.

Microgravity has provided experimenters with a unique way to remedy theseproblems: firstly by the suppression of fluid flow driven by buoyancy in the liquid andgas phases, and secondly by allowing more effective holding and controlling ofreactive melts without containers in the weightless conditions and the homogeneousdispersion of refining particles in the absence of sedimentation.

In both the formation of a solidification microstructure and in the measurement ofmelt properties, the time needed to reach the asymptotic state in an experiment isgenerally long (several hours to a day or more). Extended periods of microgravity aretherefore required. That can be achieved onboard the Space Shuttle, on a RetrievableCarrier like Eureca, on Mir, or on the International Space Station (ISS). By these meansit has been possible, for example, to obtain the unambiguous benchmark data that areneeded to distinguish between the diverse alternative 3D models that are proposed forsolidification and casting processes, in order to select the most accurate. Moreover, thereliable and precise thermophysical coefficients needed for materials engineering ormodel assessment have been measured in space experiments.

A few examples that demonstrate the soundness and value of using microgravity,together with some perspectives for potential developments over the next decade, aregiven below, successively addressing the two critical points introduced above.

2.3.3.2 Microstructure Formation in Solidification Processing

Materials-engineering research and development (R&D) is concerned with the controlof the solidification microstructure. This will include its formation during processingand, potentially, its further evolution in thermo-mechanical treatment, as indicated inthe following schematic:


For this reason, the quantitative numerical simulation of casting and solidificationprocesses is increasingly demanded by manufacturers. Compared to the well-established but time-consuming and costly trial-and-error procedure, the simulationprocess provides a rapid and cheap tool for optimising the microstructure of high-quality castings. In particular, where process reliability and high geometric-shapeaccuracy of the cast structural component are important, simulation can be veryadvantageous. Figure 2.3.3.2, for example, shows the filling simulation for a complexengine block and the associated temperature distribution. Any improvement in thenumerical simulation results in improved control of the fluid flow and coolingconditions. That enables further optimisation of the defect and grain structure, as wellas the stress distribution in critical regions of components. Moreover, through thecontrol of unwanted crystallisation events, it becomes possible to produce completelynew materials with a controlled amorphous (glassy) or nano-composite structure.

The demands on engineering materials are continuously increasing: highermechanical strengths at higher temperatures (superalloys), weight reductions (lightalloys, metallic foams), augmented lifetimes, better resistance to corrosion, reduceddevelopment times and costs, lower energy consumptions, environmentalcompatibility and materials recycling, etc. It follows that a continuing R&D effort isneeded to improve materials in these ways, as well as advanced productiontechnologies. That often implies breaking through technology barriers. In order forglobal numerical simulation to successfully contribute to that process, two aspects arecrucial:– Reliable determination of the fundamental physical mechanisms and relationships

that govern microstructure formation and selection. Indeed, complete numericalsimulation over all the length scales and complex shapes of real castings ispresently, and probably still for some time, beyond the reach of the most powerfulcomputers. These computer limitations can be overcome by using micro-macroapproaches, in which the phenomenological microstructure relationships areincorporated into macroscopic numerical simulations to bridge the small lengthscales and get rid of the fine meshing effect, which can overwhelm the computation.

– Reliable determination of the thermophysical and related properties. These arerequired as input parameters in describing balances in the volume phases (heat,chemical species, momentum ...) and at the boundaries (solid/liquid, liquid/gas ...).Together, they form a set of coupled equations whose solution, for prescribedprocess parameters and initial conditions, should realistically reproduce themicrostructure of an alloy cast under the same conditions. At present, furtherquality optimisation is limited by the lack of precision in the thermophysical dataon industrial materials. This is because of the difficulties inherent in determiningthese data, due to the high temperatures that are involved and the chemicallyaggressive nature of the melts that are in contact with container materials.

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instance, the viscosity measurements reported for pure iron, the basis for any steelproduction, differ by about 50%, as shown in Figure 2.3.3.3.

Growth transients and microstructure formation and evolution are then the centralissues, especially as many castings are the result of microstructure competition andselection (e.g. columnar versus equiaxed grains). Cast billets cool down slowly andthus are always in a time-dependent state. In industrial technologies, process controlbecomes particularly important for the growth of single crystals and complex shapes.

Even in the case of directional solidification, an established model technique thatallows microstructure formation in alloys and composites to be examined under well-defined conditions, the mere application of the pulling velocity induces front recoil,due to the building of a solute boundary layer in the melt adjacent to the solid/liquidinterface (Fig. 2.3.3.4a). It is precisely during this period that the planar front becomesmorphologically unstable. For a massive specimen, the thermal exchange between thefurnace and the sample varies significantly. Also, gravity-driven convection adds itsown contribution to the transport, so that the front withdrawal (Fig. 2.3.3.4b) is quitedifferent from what is observed in thin samples under diffusive transport and a frozentemperature field. It is therefore very complicated to analyse. The value of a real-timeand precise investigation of transients under microgravity, which is a particularly


MICROSTRUCTURE ( thermo-mechanical treatment ) PROPERTIES

CONTROL TAILORING(Materials Engineering)

The ultimate challenge is the tailoring of the dendritic grain structure and thesegregation of chemical species, formed on the scale of the whole casting during thesolidification process (Fig. 2.3.3.1), together with the fine microstructure and micro-segregation of the grains. In order to arrive at reliable microstructure relationships,pattern formation in solidification processing is being investigated under diffusiveconditions, and with fluid flow in the melt, by means of comparative experiments.

The various areas of research in this field, in which critical questions have beenaddressed, are discussed below. Some striking experimental results obtained in recentyears in space, and in preparatory ground-based work, are presented.

- Crystal Nucleation and Growth Transients

Transient stages, during which new phases may form and new patterns begin todevelop, play a central role in processing from the melt, which includes casting,welding, single-crystal growth and directional solidification. Crystal nucleation andgrowth is usually the first step, achieved by cooling the liquid below itsthermodynamic equilibrium (liquidus) temperature. Crystalline nuclei of nanometerdimensions are formed, which subsequently grow. Alternatively, if the formation ofnuclei fails to occur, then a metallic glass is formed at the glass transition temperature.

Presently, our basic understanding of the fundamentals of the nucleation of crystalsfrom the melt is generally limited to pure substances under well-controlled conditions.The main limitations for the description of the more generally used alloys stem fromthe lack of precise values for their thermophysical properties. Indeed, the basicthermophysical properties used in classical nucleation theory, such as viscosity,interfacial crystal/liquid tension and the driving force for crystallisation as a functionof temperature, are generally not known with the precision required. The analysis ofnucleation therefore currently relies mostly on circular arguments. This is even moreimportant for complex multi-component alloys, which are used for engineeringcomponents, and for highly undercooled melts, where theory generally fails.

Consequently, it is essential to measure the relevant data, as a function oftemperature, with the required precision. That data is also required for improving thecontrol of crystal growth. Indeed, for most advanced materials, the relevantthermophysical properties needed for the simulation of heat flow and fluid flow duringsolidification processes are not known, due to inherent experimental limitations. For

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Figure 2.3.3.3. Measured viscosity data for iron as a function of temperature (from T. Tanaka et al., Z. Metallkunde, 87, 380, 1996)

limited data is mostly due to timeline and/or energy constraints. Consequently, it hasnot been possible so far to carry out any comprehensive and systematic study, nor tocheck the reproducibility of the results.

It is anticipated that future research into columnar dendritic growth is likely to focuson the solid/liquid region extending from the dendrite tips to the fully formed solid,the so-called ‘mushy zone’. This is where the dendrites form, in active interaction withneighbours, and with fluid flow in the porous ‘mush’ during ground processing. Thistopic is especially critical for super-alloy turbine blades that must be single crystals


promising area of research for the ISS era, has already been amply demonstrated (Fig.2.3.3.4c) by means of the measurement of the Seebeck voltage. The Seebeck methodis a non-destructive thermoelectric diagnostic technique, based upon the solid/liquidjunction acting as a thermocouple. It was used during a series of runs at differentpulling rates on a single Sn–Bi alloy that is repeatedly recycled. This is a criticaladvantage in space, where the opportunities for sample exchange are generallyrestricted, if only because of basic security rules.

- Columnar Growth

The columnar growth (cellular and dendritic) process has repeatedly been addressedsince the earliest microgravity investigations, often with striking results, such as themillimetre-sized dendrites obtained in Al–Cu. Nonetheless, only a series of a few datapoints are available on various alloys, processed in diverse solidification facilities. The

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Figure 2.3.3.5. Columnar dendritic growth in a directionally solidified Co–Sm–Cu peritecticalloy. The view of the dendrite array is obtained by etching away the Co17Sm2 matrix fromthe primary Co dendrites (courtesy of R. Glardon & W. Kurz, EPFL)

Figure 2.3.3.4. (a) Directional solidification: the pulling velocity V determines solute flow,the thermal gradient G drives heat flow and, in the presence of gravity, they both controlbuoyancy convection in the melt. (b) Front recoil in a succinonitrile-acetone bulk sample;the asymptotic solutal recoil under diffusive transport would be at –1680 µm (fromH. Jamgotchian et al., in Proc. Symp “Utilisation of the International Space Station”, ESA,Noordwijk, 1999, p. 329). (c) The increase in the ratio of the experimental (Vc,exp ) andtheoretical (Vc,th ) values of the interface velocity at the breakdown of the planarsolidification front indicates that the recoil delays morphological instability (from J.J. Favieret al., in Materials and Fluids under Low Gravity, Springer, Berlin, 1996, p. 77)

(b) (c)

(a)

industry, a thin equiaxed grain structure that is homogeneous in all directions wouldappear to offer a convenient way of fulfilling the requirements. In practice, grainsedimentation is commonly observed on the ground (Fig. 2.3.3.7b). This undesirableeffect is suppressed in a low-gravity environment, where samples with fully regularequiaxed microstructures are obtained (Fig. 2.3.3.7a).


Figure 2.3.3.7. Equiaxed growth of refined Al–4wt% Cu alloys in microgravity, with regularequiaxed grains (a), at 1g, with a strong settling effect (b) (from M.D. Dupouy et al., in Proc.‘Modelling Welding and Advanced Solidification Processes’, TMS, Warrendale, 1998,p.415). (c) Nucleation of an equiaxed grain on a TiN particle ahead of columnar dendritesin a GTA weld of ferritic stainless steel (courtesy of H.W. Kerr)

made of a fine and regular array of columnar dendrites. Single-crystal turbine blades,with enhanced thermal-fatigue strength and creep resistance are required, forexample, by the aerospace and electrical power industries. However, thereproducibility of single-crystal growth of sufficiently large blades, particularly forstationary turbines, is rather limited and needs to be improved. Indeed, themechanical performance of these commercial cast-to-shape products can rapidlydeteriorate if dendrite misalignment, parasitic nucleation of new grains, or frecklinginduced by severe solute-driven convection, occur during casting.

In addition, the current development of facilities dedicated to studies in space oftransparent media (e.g. ESA Fluid Science Laboratory and DECLIC project at CNES) willenable the real-time and in-situ three-dimensional observation of the growth oforganic compounds by optical methods, with negligible convection. Some of thesecompounds solidify in the same manner as metals, and the data can therefore be ofrelevance for understanding the 3D behaviour of metallic melts. Numerousliquid–solid–liquid cycles can be performed on one sample, using a large range ofcontrol parameters. In the succinonitrile–acetone system, for example, convection islargely dominant at 1g, which creates a solute gradient at the solid/liquid interface.Hence, morphological instability propagates against fluid flow and a gradient inmicrostructure is ultimately observed, extending from a smooth interface to dendrites(upper-left corner) in Figure 2.3.3.6a. Recent experiments in the MOMO facilityonboard the Space Shuttle have demonstrated that detrimental effects are actuallysuppressed in microgravity, where homogenous cellular patterns do form (Fig.2.3.3.6b).

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Figure 2.3.3.6. Direct observation of the morphology of the solid/liquid interface in thesuccinonitrile–acetone system. (a) 1g: gradient of microstructure due to convection in theliquid phase (from N. Noël et al., J. Crystal Growth, 187, 1998, 516). (b) microgravity:extended cellular pattern obtained under diffusive transport (from B. Kauerauf et al., J. Crystal Growth 193, 1998, 701)

- Equiaxed Growth and Columnar-Equiaxed Transition (CET)

When, in production, a non-uniform material with dispersed properties must beavoided, such as in the investment casting of engine blocks for the automobile

(a)(b)

(c)

fundamental interest lies in the richness of nonlinear dynamic phenomena, whoseinvestigation benefits advancement of our understanding of the basic physics of out-of-equilibrium systems.

Trapped pores are another class of multiphase growth and a source of extremelydetrimental defects. They are due either to residual gas(es), causing the nucleation andgrowth of bubbles, or to the shrinkage of the solid. The solidification of metal-matrixcomposites, engineering materials in which the solid is reinforced during growth bythe incorporation of particles or fibres (e.g. alumina-zirconia fibres in an aluminiummatrix), bears similarities in the sense that the engulfing of the reinforcement is againa critical issue. Particle trapping is still a subject of active microgravity research. It is aprocess that is influenced and even prevented by fluid flow. Peritectic reactions canalso produce particles in-situ, such as the Sn3Sb2 ones (Fig. 2.3.3.8), whose formationin Sn–Sb alloy has been studied on Texus sounding rockets.


This example shows that better knowledge of equiaxed growth is imperative for thefurther understanding of the casting process. For many years, studies have thereforebeen carried out at different scale levels, ranging from the minute level of the freegrowth of a single dendrite, at the intermediate level of the envelope of a single grainembedded in its neighbourhood, through to the collective level of a set of interactinggrains. Any fluid-flow interference makes such studies much more convoluted, so thatthe ISS will be the appropriate place to continue with these experiments, and toextend them to competitive grain growth.

It will also be valuable to thoroughly investigate and precisely determine theconditions for the transition from columnar dendritic growth to equiaxed crystalformation. This transition strongly depends on seeding of the melt with solid nuclei.That is achieved either by conveying detached solid fragments of columnar dendritesinto the bulk of the liquid, or by crystal nucleation on inoculated refining particles, asshown in Figure 2.3.3.7c. For both methods, nucleus sedimentation is a limitation,against which electromagnetic/vibrational stirring is employed to promotehomogeneous dispersion of nuclei. In space, it will be possible to assess theeffectiveness of stirring processes by deliberately creating low to high fluid flow levelsin a perfectly clean and controlled way. Such experiments may require the use ofisolation mounts to reduce interference from g-jitter effects.

- Multiphase Growth and Multicomponent Alloys

The most common case of multiphase growth is certainly the solidification of binaryalloys around the eutectic composition, where coupled growth of lamellae or rods ofdifferent solid phases is observed. These eutectics are the simplest natural composites.Some such systems may have interesting mechanical properties, for example byintroducing fragile but high-strength rods into a ductile matrix. Monotectic patterns,in which rods of a second liquid phase form together with a solid matrix, are eutectics’cousins. The major difference is the presence of a number of fluid/fluid interfaces thatare known to be prone to strong surface-tension-driven convection. This phenomenonis generally of secondary importance on Earth, where buoyancy effects most oftendominate fluid flow. In space it becomes important and there it can be studied actingalone. Furthermore, monotectic systems with concentrations in the liquid miscibilitygap, where droplets of the second liquid phase form in the melt, have potentialapplication in car bearings where, once solidified, the droplets provide lubricating softinclusions (e.g. Pb, Bi, in a hard matrix).

Peritectic systems are those in which a second solid phase forms by reaction betweenthe melt and a first solid phase. They are of both practical and fundamental interest.The former follows from studies of the peritectic reaction, which are making a stepforward towards real commercial multi-component alloys (e.g. steels) that form morethan one solid phase, often in a sequence along the solidification path. The

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Figure 2.3.3.8. Cross-section of an Sn–13 at%Sb sample solidified in microgravity duringthe Texus-34 mission. The peritectic phase is directionally solidified from the left until themarker (white lines). The properitectic Sn3 Sb2 phase is dispersed in the whole samplebecause there is no sedimentation in microgravity (from Th. Kammler, VDI-Fortschrittsberichte 487, VDI Verlag, Düsseldorf, 1997)

Figure 2.3.3.9. Schematics of a polycrystalline structure, with long-range crystalline order,and an amorphous atomic structure, with short-range liquid-like order

low as 1 K/sec are sufficient to obtain high levels of under-cooling and produce a bulkglass for a number of pseudo-eutectic Zr-based alloys. This is illustrated in Figure2.3.3.10.

Analysis of the different microstructures that can be achieved in the pseudo-ternary(Zr41Ti13)(Cu13Ni10)Be23, under different cooling and annealing conditions, revealsthat a broad range of length scales are available. They are controlled by nucleationand growth kinetics under the appropriate processing conditions. Figure 2.3.3.10exhibits two different microstructures as typical examples. For the same material, withidentical chemical composition, a multi-component phase mixture with several (fivestable and metastable) intermetallic compounds is obtained by crystallisation justbelow the eutectic temperature (length scale of 0.1 mm, Fig. 2.3.3.10a). A nano-crystalline microstructure is obtained by thermal annealing of the glass (length scaleof about 50 nm, Fig. 2.3.3.10b). The cast material (a) is extremely brittle, whereas thenano-structured material (b) has excellent mechanical properties. The maximummechanical strength of the glass is 1.5 to 2 GPa under both tension and compression,which is more than double that of conventional crystalline metallic materials. It israther typical for refractory ceramics, but they do not have good mechanicalproperties under tension due to their brittle nature.

2.3.3.3 Thermophysical Properties and Containerless Processing

The paucity of thermo-physical property data for both commercial materials andthose of fundamental interest is a result of the experimental difficulties that arise athigh temperatures. As discussed earlier, knowledge of these properties is essential forthe understanding and subsequent modelling of metallurgical processes, forthermodynamic phase equilibria and phase-diagram evaluation. Thus, accurate inputdata are needed for the stable liquid and at different levels of liquid under-cooling.

Some of these data can be obtained more or less accurately by conventional methods.High-precision measurements, however, on chemically highly reactive melts at thetemperatures of interest, require the application of containerless processing usingnon-contact diagnostic tools.

- Containerless Processing

By eliminating the contact between the melt and a crucible, accurate surfacenucleation control and the synthesis of materials free of surface contaminationbecome possible. For highly reactive metallic melts, electromagnetic levitation (EML,Fig. 2.3.3.11) is a well-developed containerless technique. It offers several advantagesover alternative levitation methods due to the direct coupling of the electromagneticfield with the sample. In microgravity, the considerably reduced electromagneticpower-input requirement for levitation allows processing under ultra-high-vacuum


- Glass Formation

If crystal nucleation in the under-cooled liquid can be avoided completely below theliquidus temperature, the liquid eventually freezes into a non-crystalline solid – a glass(Fig. 2.3.3.9). Glasses have of course been manufactured from silica and related oxidesfor thousands of years. More recently, by developing new alloys and processingtechniques, it has become possible to produce more and more materials in anamorphous form. These have superior properties compared with their (poly)crystallinecounterparts, including materials with covalent (Si-based), van der Waals (polymers)and metallic bonding.

In particular, the new metallic glasses that can now be produced in large dimensionsand quantities, the so-called ‘bulk metallic glasses’ or ‘supermetals’, are becoming animportant industrial and commercial material. They are superior to conventional Ti-,Al- or Fe- based alloys. They have about twice the mechanical strength (about 1.8 GPa)of conventional materials, excellent wear properties and excellent corrosion resistancedue to the lack of grain boundaries. These advanced materials can now be producedwith dimensions of several cubic centimetres by casting or by zone meltingtechniques under high-vacuum conditions. In order to develop and optimise thecasting process for the production of these new advanced materials, a number ofmeasurements have been performed in microgravity during the recent IML-2 and MSL-1 space missions.

Due to their strong resistance to crystal nucleation and growth, the control ofmicrostructural development is unique for metallic systems. By varying cooling ratesand using different heat treatments, the range of microstructural length scales cannow be varied by several orders of magnitude, extending from regular eutecticmicrostructures to the nano-crystalline and glassy state. For instance, cooling rates as

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Figure 2.3.3.10. Variation of microstructural length scales in multi-phase samples with theidentical chemical composition Zr41Ti13Cu13Ni10Be23. Sample (a) is crystallised at smallunder-cooling (length scale 100 µm), while sample (b) corresponds to an initially glassysample annealed and crystallised at 600°C for 5 hours (length scale 1 µm)

- Experimental Results under Microgravity Conditions

New sophisticated methods of controlled levitation, diagnostics and data analysishave been developed for the study of liquid samples of 7 – 10 mm diameter inmicrogravity. These methods allow the direct measurement of:

– melting range– solid-fraction/liquid-fraction during casting – heat capacity and enthalpy– density – surface tension – thermal conductivity and diffusivity – viscosity – total hemispherical emissivity and other optical properties– electrical conductivity.

Given the limited space available here, only some of the most important results can bepresented, in particular for the newly developed bulk metallic glass-forming alloys.Such measurements have not been possible in the past and represent some of themost impressive results from recent microgravity research.


conditions, with a much extended temperature range (700 – 2700 K) and bettertemperature control (T-measurements better than 0.1 K) of a quiescent liquid sample.

Based upon the successful development of containerless processing and diagnosticmethods in space, high-precision measurements of critical and reactive melts at hightemperatures are now becoming possible. These avoid any chemical reaction of thespecimen with a containing environment. However, the required high accuracy canonly been achieved when the following conditions are fulfilled:– Extended processing periods (> 10 000 sec).– Ultra-high-vacuum conditions (better than 10-8 torr).– Minimised levitation forces and thus controlled heating and reduced liquid

convection compared with 1g gravity conditions on Earth.– Sophisticated analytical tools.

These conditions can be only fully satisfied in a long-duration microgravityenvironment. Based on the positive experience with recent long-term spacecraftmissions and several hundred hours of processing time, new scientific methods as wellas equipment modifications are being developed. These will allow the precisedetermination of the much-needed temperature-dependent data for highly reactivemelts. This, in the future, will allow considerable improvement of existing materialsprocessing technologies, as well as the development and application of new advancedmaterials, e.g. glassy ‘supermetals’ and other lightweight and high-strength materials,with controlled micro-or nano-structures.

During the earlier Spacelab missions, the thermo-physical properties of chemicallyreactive metallic liquids have been measured with a precision that had hitherto beenunattainable. Some of the experimental results obtained for this new class of‘supermetals’ from recent space flights are discussed below.

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Figure 2.3.3.11. Schematic of the electromagnetic containerless processing facility, withpower modulation inducing a controlled temperature modulation on the hot sample

Figure 2.3.3.12 shows the experimental temperature versus time profile for the alloyZr65Al7.5Cu7.5Ni10. This gives the melting range and a liquid under-cooling level of 194K. Modulation of the power and hence of the resulting temperature allows determination of the specific heat (Cp) of the liquid sample, as shown in Figure 2.3.3.13

From similar experiments during the crystallisation plateau, the enthalpy ofcrystallisation has been determined, as well as the solid/liquid fraction as a functionof time. Furthermore, the electrical resistivity ρ (which relates directly to the thermalconductivity λ, being proportional to T/λ) has been measured as a function oftemperature in this alloy for the first time. The results are shown in Figure 2.3.3.14.

The total hemispherical emissivity ε of this multicomponent alloy is shown in Figure2.3.3.15, where there is an unexpected change (maximum) close to the meltingtransition. The temperature dependence of the total hemispherical emissivity of theliquid sample, when combined with measurements of the electrical resistivity, allowsobservation of surface segregation effects or solution of a surface impurity phase, asa function of temperature. This offers a new approach for the investigation of surface-related chemical processes. In another set of experiments on different samples, high-precision measurements have been carried out to obtain the viscosity and surfacetension.


Figure 2.3.3.13. Specific heat (Cp) data for microgravity experiments (liquid sample red) and1g experiments (crystalline sample black, glassy sample blue)

Figure 2.3.3.14. Electrical resistivity of the Zr65Al7.5Cu7.5Ni10 alloy in the following states:liquid (triangles), glass (upper) and crystalline phase mixture (lower curve)

Figure 2.3.3.15. Total hemispherical emissivity (ε) as a function of temperature for a Zr-Al-Cu-Ni-Co sample

Figure 2.3.3.12. Temperature/time profile of a glass-forming alloy sample with high-precision temperature modulations for heat-capacity measurements in the under-cooledliquid (below 1163 K)

solidification in primary and secondary refining, casting and foundry operations, dipcoating and welding operations. Many of the models started out as ‘expert systems’correlating known practice information, but more exact models have been developedto provide analytical insight. It is important in all industries to ‘get it right the firsttime’, but it is especially important in the foundry and casting industry, in order tominimise working time and material wastage.

It follows, therefore, that companies express a real interest in the continuation ofmodel developments and their application to processes. In particular, jointapplication-oriented efforts with industry on scientifically well-defined problems andon the extension of basic research to materials engineering are spreading rapidly. Astriking example is the development within a consortium of industries, with Europeanand North American members, of three-dimensional numerical simulation of thedendritic grain structure at the scale of the whole casting. Also, industry is presentlysupporting the simulation of the directional casting of large gas-turbine blades.However, it should be emphasised that, although the effects of fluid flow on theformation of microstructure (columnar mushy zone, equiaxed grains) have beenincorporated into the models (Fig. 2.3.3.17), their implementation into the predictivesoftware that is used by industry is still in its infancy. This is due to the severelimitations and the hypotheses that have to be made in the interests of tractability. Forinstance, the type of interaction between a dendritic grain and its surrounding liquid,needed to model the movement of the solid, is poorly described.

Beyond the direct interest emanating from processing, industries also recogniseupstream experimental and theoretical research on fundamental points as amandatory requirement in order to develop conceptual tools. For instance, analuminium company awarded a grant to a PhD student to merely observe thesedimentation of an equiaxed dendritic grain in a transparent model system. The needfor basic research motivated by bottlenecks in applications is further evidenced by thecritical topics addressed at the EUROMAT ’99 Congress on advanced materials andprocesses, with a number of sessions chaired by representatives of commercialcompanies.

Equally, reliable and high-precision thermophysical property data are important forprogress in casting. It has been clearly shown recently that the prediction of defects incastings can be significantly improved by replacing estimated thermophysicalproperty data in the software with experimental values for the particular alloy. Ingeneral, companies are dissatisfied with the amount of data available for commercialmaterials and new alloys. This includes primary metals producers, secondary refiners,as well as end users. Furthermore, the response to a questionnaire distributed withinEuropean industry has indicated an urgent need for high-quality data onthermophysical properties to: gain a better understanding of solidification, and solveproblems encountered with the process in order to improve product quality and


One of the most important results has been the determination of the integral drivingforce for crystallisation for different compositions of glass-forming alloys, based uponthe above measurements (specific heat, heat of crystallisation / melting). This isindicative of the stability of these glasses and is shown in Figure 2.3.3.16. Severalchemically highly reactive alloys have been investigated in the microgravityexperiments. A clear correlation has been established for the first time between thestability of the metallic glass (against crystallisation) and the energetic driving force forcrystallisation, based upon selected experiments performed in microgravity.Furthermore, the entropic instability temperature (arrows in Fig. 2.3.3.16) tends to behigher with increasing stability (lower driving force) of the metallic glass.

2.3.3.4 Views from European Industry

Obviously, the improvement of casting control, efficiency and product quality headsindustry’s wish list. For example, the steel industry uses more than 20 mathematicalmodels in steel production. There are several types of models (predictingthermodynamics, kinetics, fluid flow, etc.), but models combining fluid flow andtransfer of heat and species in calculations have proved particularly useful in a widespectrum of processes involving solidification. They have been applied to the

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Figure 2.3.3.16. The Gibbs free energy difference of the under-cooled liquid correspondingto the driving force for crystallisation and the relative stability of the bulk glass formingalloys 1 to 6. Curve 1: Zr64Ni36 with an estimated critical cooling rate of Rc > 105 K/sec.Curve 2 : Ti34Zr11Cu47Ni8 with Rc ≈ 250 K/sec. Curves 3 and 4: Zr65Al7.5Cu17.5Ni10 andZr60Al10Cu18Ni9Co3 respectively. Curves 5 and 6: Zr57Nb5Cu15.4Ni12.6Al10 andZr41.2Ti13.8Cu12.5Ni10Be22.5 with Rc ≈ 10K/sec and Rc ≈ 1K/sec, respectively

minimise waste and energy costs. As a result of this wide survey, the properties citedin Figure 2.3.3.18, which are mostly unknown for commercial materials, areconsidered important in the corresponding hierarchy. These properties are identicalwith those measured during Space Shuttle missions on highly reactive materials.

Important examples of relevant industrial processes that must still be improved are:– Casting processes (Fe-, Ni-, Ti-, Al-, Mg- alloys, refractories, metal-matrix composites).– Crystal growth of poly- and single-crystalline materials (turbine blades and discs,

semiconductors).– Glass production (metallic and non-metallic).– Rapid prototyping.– Spray forming and powder production.– Surface modification by laser and spraying techniques.– Welding (conventional, laser, electron).


Figure 2.3.3.17. (a) Longitudinal cross-section of an aluminium-base alloy cast ina steel mould (120 mm high and 60 mm indiam.). A sedimentation cone of fineequiaxed crystals is clearly seen at thebottom of the ingot, as in Figures 2.3.3.1and 2.3.3.7b, and a coarse columnarstructure at the top (from N.L. Cupini et al.,in ‘Solidification and Casting of Metals’,Metals Society, London, 1979, p. 193).

(b,c) Numerical simulation of the CET in aconventionally cast Al-7wt%Si alloy (b)without and (c) with grain movement(courtesy of Ch-A. Gandin et al.). Whenallowed to move, equiaxed grains notlinked to the mould wall are transporteddownwards by fluid flow and bysedimentation, and the picture is inagreement with experiment. (Thesimulation without grain movement isqualitatively similar to equiaxed growth inmicrogravity; see Fig. 2.3.3.7a)

Figure 2.3.3.18. Results of a survey of European (here UK) metal-production businessesconcerning the significance of the thermophysical properties of liquid multi-componentalloys

(a)

(c)

(b)

temperature. Moreover, cheap and flexible sounding-rocket experiments on simplifiedconfigurations may still be useful for preliminary studies in short periods ofmicrogravity throughout the ISS era.

Among other objectives, two are clearly at the forefront, as they urgently requireprogress. In columnar growth, the understanding of the dynamics of formation andstability of the dendritic ‘mushy’ zone is a real challenge. Indeed, the time-dependentbehaviour of this zone, with fluid flow and formation of solute freckles, is common inmost industrial casting processes. It remains badly understood. In equiaxed growth,benchmark data must be generated under purely diffusive through to increasinglyconvective transport conditions, to validate models for predicting grain structures incastings. The United States is significantly ahead in the preparation of spaceexperiments in which several equiaxed dendrites are interacting.

- Reliable and Precise Measurements of Thermophysical Data

These are a prime goal in order to improve the modelling of industrially relevantsolidification processes. Although the standard Earth-based techniques appear towork for several materials, they cannot be confidently applied to reactive melts at hightemperatures, due to contamination and exothermic reactions from the cruciblesrequired to hold the liquid samples against gravity. New scientific methods, as well asequipment developments, are now available which permit containers to be eliminated.Further increases in accuracy will be possible by carrying out these measurements inthe microgravity environment of space, under ultra-high-vacuum conditions.

High-precision experiments have been successfully carried out in an electromagneticcontainerless processing facility (EML/TEMPUS) during several Spacelab missions. Ithas been demonstrated that the reduction of positioning forces in microgravity eitherleads to a significant improvement in accuracy or permits measurements that areotherwise impossible. These new experiment techniques can be extended to measurethe thermophysical properties of liquid materials that are of commercial interest. Theyopen a new research field of high-precision thermophysical property measurements,and their application for high-precision numerical modelling of industrial castingprocesses. For the future, an experimental programme in a containerless processinglaboratory on the International Space Station is planned. This will allowmeasurements on samples of industrial and technological interest using non-contactdiagnostic methods.

The knowledge gained in earlier ground and microgravity studies, taken together withthe outcome of the experimental, theoretical and numerical investigations thatmaterials scientists are completing, is now generating an ambitious and coherentprogramme of critical experiments destined to be carried out in the low-gravityenvironment of the ISS. By that process of deepening the fundamental understanding


2.3.3.5 Conclusions and Perspectives

Due to the extreme complexity of casting processes, their numerical simulation islargely split into several segments at present, each of which is tackled by ratherseparate communities. In order to advance the use of efficient and user-friendly globalnumerical simulation of processes with integrated codes, it is essential to strengthenthe coupling between those researchers working on the microscopic scale and thoseworking on the macroscopic scale. This might be achieved, for example, by associatingin a dedicated research programme physicists working on the microstructure scale,metallurgists and process engineers preoccupied with the whole product, andchemists determining the required thermophysical properties.

The microgravity environment provides the conditions that enable unambiguousreference studies to be undertaken of the basic contributions to the formation of thesolidification microstructure, as well as measurements of melt properties, withoutcomplicating artefacts from fluid flow. Moreover, the use of the ISS as a laboratory willenable comprehensive studies and flexible experiments. That type of usage will begreatly facilitated by telescience supervision and interactive control of theexperiments from the ground.

As far as industry is concerned, they seem ready to finance simulation-based projectson microstructure formation of solidifying melts, and experimental programmes ontechnical alloy systems, but most remain to be convinced of the need to invest in amicrogravity programme per se. The returns from such research are perceived to betoo distant on an industrial time scale.

In research terms, the prime goals for the future are:

- Reliable Determination of the Fundamental Relationships, at Microstructure Scales

The strategy is based on a joint attack on open questions, using approaches thatcombine well-defined experiments with theoretical and computational modelling atmicrostructure and intermediate scales. Furthermore, R&D people are now convincedthat the clarifying of the intricate effects encountered in processing necessitatesrecourse to model processing. By ‘model’ is meant a simpler process (e.g. directionalsolidification instead of regular casting) or/and a simpler alloy system (e.g. binaryNi-based alloy in place of a real superalloy).

There is undoubtedly a definite advantage to be gained if scientists can start buildingthe future on well-adapted space facilities. Indeed, for the ISS utilisation phase, ESAand national space agencies already have a first series of facilities and diagnosticsunder development for metallic systems (LGF and SQF for low- and high-melting-pointsystems, respectively) as well as for transparent analogues melting at about ambient

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2.3.4 Heat Transfer and the Physics of Fluids

W. Grassi & J.C. Legros


The study of the science of heat transfer during the latter part of the 19th Century wasfundamental to the formulation of the Principles of Thermodynamics. It led towardsPlanck’s radiation theory and was an important factor in the analyses that eventuallyled to quantum physics. Nowadays, it also plays a key role for terrestrial and for spacetechnology and has a crucial impact on the social and economic development ofmodern countries. In those countries, there is a growing awareness of the importanceof the climate change that can be caused by human activity, particularly with regardto the production of greenhouse gases, e.g. CO2, CH4, NO2, CFCs. These are mostlyassociated with the products of energy- and heat-transfer technologies.

The 17th Congress of the World Energy Council, held in Houston in 1998, focused onhow technology could face the challenges of energy supply and use in the comingdecades. Four main mandatory requirements were pointed out by the Council: – ‘increasing the efficiency of both the supply and use of energy, in order to mitigate

the environmental impact, including climate change, and to improve the economiccompetitiveness’

– ‘reduction of local pollution ...by using more energetically efficient equipment’– ‘facing the problem of climate change with more efficient technologies for the use of

fossil fuels’. It was also stressed that: ‘..The increased efficiency in the use of energyconstitutes the most immediate, wide and economic opportunity of reducingresource consumption and environment degradation’, and that ‘Efficiency shouldbecome mandatory in any aspect of the energy business..’

As most of the energy-dedicated equipment involves heat transfer, the enhancementof the efficiency of heat-exchange performance is a fundamental requirement. Withinthe field of fluid physics, the most effective heat-exchange technologies are thoseinvolving phase changes and, in particular, evaporation, boiling and condensation.Their use on Earth is obviously very widespread and includes power generationplants, cooling of electronics, building air conditioning, food conservation, etc.Consequently, their importance in daily life and their economic impact are clearlyenormous.

The question then arises: ‘How can fluid-physics research in low gravity contribute toimproving energy efficiency for ground-based equipment and thereby reduce


and providing highly precise measurements of thermophysical properties, these spacestudies can confidently be predicted to contribute substantially to the progress ofmaterials development and processing, and thus ensure the future competitiveness ofEuropean industry.

Acknowledgements

Thanks go to the members of the ESA Topical Team ‘Thermophysical Properties ofLiquids’, particularly Dr. K. Mills, Dr. I. Egry, and Prof. P. Desreé for critically reviewingthe manuscript, and the ESA Topical Team: ‘Convection and Pattern Formation inMorphological Instability during Directional Solidification’, and particularly thecontributions by Prof. J. Hunt, Dr. D. Camel, Dr. G. Zimmerman, Prof. K. Kassner andProf. A. Wheeler. Grateful thanks also go to Dr. Ch-A Gandin for stimulating exchanges.

Further Reading

Condensed Matter and Materials Physics: Basic Research for Tomorrow’s Technology,National Academy Press, Washington, 1999.

EUROMAT ‘99 Proceedings, Wiley-VCH, Weinheim, 2000.

Herlach D., Cochrane B., Egry I., Fecht H.J. & Greer A.L., 1994, Mat. Sci. Rev., 38, p. 271.

Hurle D.T.J. (Ed.) 1993 and 1994, Handbook of Crystal Growth, Vols. 1b & 2b, North-Holland, Amsterdam.

Ratke L., Walter H.U. & Feuerbacher B. (Eds.) 1996, Materials and Fluids under LowGravity, Springer, Berlin.

Walter H.U. (Ed.) 1987, Fluid Sciences and Materials Science in Space, Springer, Berlin.

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Various very interesting projects have been carried out in space that have providedaccurate measurements of these coefficients in molten salts, in metallic alloys, inisotopic mixtures and in organic mixtures. Such accurate values are needed to try tochoose between the many different theories that aim to predict the diffusionbehaviour of such materials. The debate between specialists on these differenttheories is not yet closed. The established (but still not proven) representation of liquiddiffusion data in the literature is normally by an exponential ‘Arrhenius’ equation.Uncontrollable convection, from small temperature gradients or other spurioussources (e.g. Marangoni convection, separation processes, electromagnetic effects,etc.) was supposed to be at the origin of the uncertainties in the data.

Microgravity experiments on liquid diffusion were the first to show that convectioncould be mostly eliminated by using this highly-reduced-gravity environment, andthus reproducible data with very low scattering (0.5 – 2%) could be obtained.Additionally, these new space results were smaller than the 1g data, as a result of theabsence of normal convection that contributed to the disturbance of the classicalterrestrial data. Hence, microgravity results are thought now to finally open the wayto accurate measurements of the actual atomic diffusion.

Industrial ApplicationsReliable atomic liquid diffusion data are vital for computer simulations of, for example,industrial solidification or crystallisation processes or other diffusion-controlledprocesses, as discussed in Sections 2.3.1.2 and 3 above. There is a great need for suchdata for many industrial materials. Accurate data are essential, because in modernsimulations the convection and the atomic diffusion transport are treated separately.

So far, only microgravity measurements appear to provide the possibility ofdetermining the pure atomic diffusion coefficients, although different teams areinvestigating the damping influence of magnetic fields in order to curtail the disturbingconvection motions in terrestrial experiments. The damping of strong motions isactually observed by this means, but the scattering in the data in those diffusionmeasurements still persists. This indicates that some slow convection was still presentand that this disturbs the measurements. Evidently, this technique has to be furtherinvestigated in detail in the future and improved by comparison with microgravitydata. Hence, for the foreseeable future (about 5–10 years), accurate diffusionexperiments will necessarily have to be performed in microgravity conditions.

The theoretical description of diffusion and thermodiffusion is considerably moredifficult in the case of complex systems. Unfortunately, these are often the types ofmaterials in industrial use. In those cases, even a usable phenomenological approachstill lies in the future. For materials of that type, the only recourse is to the use ofexperimental diffusion coefficients, determined using microgravity conditions.


environmental pollution?’ In order to answer that, the following discussion willintroduce some of the basic concepts in heat transfer and the behaviour of fluids inmicrogravity conditions. It will then consider some of the relevant space experimentsthat have been performed and the ideas for future experimentation on theInternational Space Station (ISS).

2.3.4.2. The Physics of Fluids, Heat Transfer and Diffusion

The scientific and engineering motivation for conducting low-gravity experiments onthe physics of fluids is either:

– To eliminate (or at least to substantially reduce) the influence of gravity on themotions (convection) in a mass of fluid: this allows the behaviour of fluid systems tobe investigated when the transport of mass and of heat are not disturbed byconvection (in the so-called ‘diffusive or conductive regime’).

– To study the motions induced by surface-tension differences along an interfaceseparating two non-miscible fluids, the so-called ‘Marangoni convection’. On Earth,in normal laboratory measurements, this contribution is often neglected, mainly because it is difficult to quantify its effect.

- The Measurement of Diffusion Properties

The diffusion coefficient is defined as the ratio between the mass flow flux of acomponent and the concentration difference existing between two points in a system.In a binary liquid solution (the only one considered here), a component is alwaysdiffusing from the high towards the low concentration point. Diffusion allows systemsto relax any concentration non-uniformity, without resorting to convection flows. It isa slow process. If a concentration difference is established over a distance of 1 cm, itwill take typically 104 – 105 sec to become homogeneous.

The thermodiffusion (also called the ‘Soret effect’ in liquids) corresponds to asegregation that takes place in a solution subjected to a temperature difference. Thecharacteristic time is also long (it obeys the same law as diffusion). The densityvariation resulting from this segregation can be of the same order of magnitude as thethermal expansion.

The long characteristic times associated with these two processes imply that any slowmotion (a few microns/sec) can disturb a concentration field. The unique opportunitythat is offered by a microgravity environment is to practically eliminate any suchdisturbing motions inside these non-homogeneous (in temperature and/orconcentration) fluid phases. Consequently, researchers have taken advantage of theseconditions, to measure the fundamental diffusion properties to an accuracy that ispotentially higher than can possibly be achieved under terrestrial conditions.

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of higher surface tension, an action that can be compared with the effect of a pressuredifference triggering a flow through a pipe. This motion, induced at the interface wherethe surface tension is acting, is also propagated into the bulk, due to the viscosity (ordrag) of the underlying bulk liquid, as shown schematically in Figure 2.3.4.1. Theresulting convection flow velocity can be rather large.


Petroleum exploration and production companies are now requesting highly accuratefluid characteristics, as parameters to be used in increasingly sophisticated computermodels. In a technical and financial context, the search for an optimal developmentscheme for a given reservoir requires knowledge of the effluent composition and itsevolution during production. Reliable and accurate values of diffusion and thermo-diffusion coefficients for those complex fluids are therefore needed in order to predictthe optimal recovery scenario. The lack of data in this field is severe.

In collaboration with Total–Fina–ELF Exploration and Production, a scientific teamfrom Europe and Canada, supported by ESA and the Canadian Space Agency, isconducting an ambitious programme aimed at providing such data for different crudeoils. Presently, instruments for carrying out the first experiments to measure diffusion(DCCO – Diffusion Coefficient of Crude Oils) and thermodiffusion (SCCO – Soret Coefficientof Crude Oils) are being developed for a Shuttle GAS (Get-Away Special) independentexperiment container campaign. A feasibility study of an instrument to be installed onthe International Space Station has begun. This programme will be supported by ESAthrough its Microgravity Application Promotion (MAP) Programme.

- Surface Tension and Marangoni Convection

Surface tension is a force per unit length, acting at the interface separating two non-miscible fluids. It is responsible, for example, for the creeping of liquid along thewettable walls of its container. A meniscus can therefore be observed at the contactline between water and the glass wall of a container. In a glass tube of small diameter,the height of the meniscus results from the balance between surface tension at theedge of the liquid column and the pull of gravity.

Surface tension results from the work that has to be performed to bring, in thisexample, a molecule from the bulk of the liquid volume towards the surface. Inside theliquid, a molecule is attracted by close neighbours in the three-dimensional space.However, the process of forming a surface creates an imbalance in these forces, sinceat the surface the close neighbours are attracted only from the liquid side (the gasmolecules being in general too far away to generate a significant attraction). It is thusnecessary to do some work against this inward attraction, in order to bring moleculestowards the surface when its area is increased.

As the compressibility of liquids is generally very small, the surface tension dependsonly very weakly on the pressure. It generally decreases with temperature. Forsolutions, changes in concentration can cause rapid and large variations, especially forlow-solubility components that are called ‘surfactants’ and are familiar as detergents.

Marangoni convection arises when there is a variation in the surface tension along aliquid surface. It produces motion from regions of low surface tension towards those

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Figure 2.3.4.1. The development ofMarangoni convection. A gradientin the surface tension at thegas/liquid interface from the hot(lower surface tension) to the cold(higher surface tension) liquidinduces a surface flow that tendsto drag the underlying bulk liquidwith it. The resulting Marangoniconvection flows in the oppositedirection to the normalbuoyancy(gravity)-induced flow.(courtesy of E. Messerschmid)

An observable example of this process happens in the liquefied wax of a burningcandle. It is easy to follow the trajectories of soot particles moving near the surfacefrom the hot region at the wick towards the colder periphery and coming backtowards the wick near the bottom of the liquid wax. These particles are following thetoroidal cellular Marangoni flow induced by the temperature difference along theliquid/air interface.

Marangoni convection can play an important role in various areas of materialsscience. It is also important within the technology domain in many processesinvolving a non-isothermal interface (see Sections 2.3.2 and 2.3.3). A typical exampleof the research effort in this field is the intensive modelling that is pursued to describeand predict the transport of heat and matter by the convective motions in the molten-zone technique, used for the production of high-quality crystals. There is a direct linkbetween the quality of the produced crystals and the control of the flow, which has tobe as steady as possible. Indeed, depending on the thermal constraints imposed onthe system, the properties of the flow in the liquid phase are different. They range fromthe steady to the oscillatory regime, or from a single convection cell to multi-cellularflow or to turbulence. The transitions between these different regimes also give rise tonew and fascinating problems linked to the spontaneous organisation of inertmaterials by fluxes of energy – what Prigogine has called ‘dissipative structures’.

In industrial processes, Marangoni convection reinforces or competes against thenormal buoyancy-induced convection. It is very important to analyse accurately the

(liquid ammonia) is pumped by the capillary effect, i.e. by virtue of surface-tensionforces, in porous evaporators. This system has the considerable virtue that it does notinvolve any moving parts or consume any energy.

In 1994, a two-phase loop experiment called TPX was flown onboard the Space Shuttlein a GAS canister. Sabca (B) was responsible for the capillary-pumped loop. Theobjective of this loop test was to demonstrate the loop’s heat-transport potential andits behaviour under different heat loads and heat sinks in microgravity. The TPX post-flight analysis showed that the loop worked correctly in microgravity conditions. Thecapillary pump developed by Sabca was a nickel porous rod with a 2.2 µm porediameter, a permeability of 5x10-14 m2 and a void fraction (porosity) of 71%. Such acapillary material is able to sustain a static head of 6.4 m of liquid ammonia.

The development of such systems is continuing, supported by parabolic-flightexperiments and the intended GAS container missions. For instance, two-phase loopsare being investigated on the Stentor satellite, supported by a CNES contract and withthe participation of Matra and Alcatel. It aims to be a flight demonstrator for newspace technologies, one of which is a new active-antenna concept developed byAlcatel, which has to be temperature-controlled. It has also to demonstrate the capabilitiesof capillary-pumped loops for large satellites in which the dissipated powers areforeseen to be about 20 kW (e.g. Alcatel’s Spacebus-4000 line).

Traditionally, the investigation of two-phase flows was conducted by the oil industry,focusing their efforts on flow through long pipelines for the transport of a mixture ofcrude oil and gas from the well to the treatment plant. The nuclear industry, from itsviewpoint, was interested in the stability of the flow to avoid drying out of the heat-exchanger loop. The chemical industries are interested in the investigation of two-phase systems with very complex geometries, for example in two-phase reactors ordistillation columns. In these cases, the Marangoni convection can be induced by bothtemperature and concentration differences.

Pioneering studies were performed already on the Spacelab mission in 1985, with theMACO (Marangoni Convection and Mass Transfer from the Liquid to the Gas Phase)experiment, led by a team from Groningen University (NL). This technologicallyadvanced experiment was followed by investigations using parabolic aircraft andsounding-rocket flights (Maser-1 and Maser-2).

A project supported by ESA (through its MAP programme) is dedicated to studying theinfluence of evaporation on convection motions. Called ‘CIMEX’ (Convection Inducedby Mass Exchange), it is led by the Microgravity Research Centre of the Free Universityof Brussels. Five topics will be investigated:– Identification and understanding of the different mechanisms that result in

convective motions in an evaporating liquid phase.


effects of their joint interactions in ground-based processes. Microgravity is a tool well-suited for the careful and accurate study of the surface-tension-induced phenomenathat are very difficult to isolate in terrestrial laboratories, and where they aredisturbed, even shielded, by gravity effects. This situation will be encountered again inthe later discussion of the very important boiling phenomena.

- Two-Phase-Flow Research

For a single fluid phase (liquid or gas) flowing in a tube, there are basically two broadcategories of flow structures: laminar or turbulent. In the laminar regime, the flow rateis proportional to the pressure difference applied. When a liquid and a vapour phase(gas) are both forced to circulate in a pipe, this two-phase flow presents a wider rangeof complex regimes, depending upon the relative distribution of the gas in the liquid,e.g. bubbles to slugs to an annular regime where the liquid flows only along the wall,plus all of the intermediate situations. As the gas phase and the liquid have verydifferent densities, their relative positions in the tube depend upon the orientation andamplitude of the gravity field. The total mass flow rate therefore now depends alsoupon gravity and on these different flow regimes. It is no longer determined solely bythe pressure difference.

In the past two decades, several gas/liquid flow experiments have been conductedunder microgravity conditions. Space applications, such as in life-support systemsand thermal-energy transport, have revealed technical problems that have stimulatedthe development of two-phase flow research in microgravity. The main topics beingaddressed are the prediction of flow patterns, pressure drops, heat transfers andphase fractions in thermo-hydraulic systems. Detailed understanding of the flowregimes is necessary in order to design space systems efficiently. This type of researchis crucial to the area of heat-transfer technologies. In such processes, the heatproduced in one part of the system evaporates some cooling liquid. The vapour is thentransported with a very small pressure drop (and thus isothermally) towards acondenser, where the heat is released. In this condenser, vapour and liquid co-exist.The efficiency of the condenser, as mentioned earlier, depends upon the two-phaseflow regime that is taking place.

The management of two-phase systems is difficult, especially in a reduced-gravityenvironment. For high heat-flux transport, such as in the electronics in the nextgeneration of large telecommunications satellites, there is no question of a choicebetween a single- or a two-phase system. Circumstances will dictate that some form oftwo-phase system must be accommodated.

A very interesting solution for transferring the degraded electrical energy (heat) fromthe core of a telecommunications satellite towards external radiators has beendeveloped by a few companies (Matra and Sabca on the European side). The fluid

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must be taken into account. In addition, a steady dynamic and thermal regime mustexist, both in the bulk fluid and at the heater.

While all of these conditions can be easily attained on Earth (in some cases, like flowboiling, on a large length scale), great care has to be paid to their fulfilment during low-gravity experiments. The physics involved is very complex, as several aspects play asignificant role. For example:– vapour–solid and liquid–solid interactions that occur on the heater, thus implying

wettability (static and dynamic), thermal conjugate conditions, liquid and solideffusivities, etc.

– the presence of an ‘elastic interface’ between liquid and solid, with a phase changeat the interface and a thermal gradient there that can create Marangoni flows

– fluid-dynamics of deformable bodies (bubbles or, in general, vapour masses) andtheir reciprocal interactions.

Consequently, a satisfactory description of the whole phenomenon, in terms ofconservation and constitutive equations (plus obviously boundary and initialconditions), is not achievable at present. The result is that current industrialengineering design of such systems is based upon simplified correlations ofexperimental data, with a limited validity range.

No doubt over the next decade an increase in computing power will make it feasibleto replace, or at least supplement, the correlations by large-scale models. Thedevelopment of successful models depends upon gaining a detailed understanding ofthe physics of boiling. The attainment of that goal can be greatly assisted byexperiments in low gravity. In particular, they can play a fundamental role by allowingthe balance between gravity-dependent forces and other interacting forces to bevaried and the results observed.

According to the classical relations, bubble flow and vapour/liquid interfacebehaviour are entirely dominated by gravity. As a consequence, the related heat-transfer correlations generally include a dependence on gravity, in almost any pool-boiling regime (see accompanying panel). The experiments carried out in low gravityhave demonstrated that this dependence of boiling on gravity is not completely true.Roughly speaking, these experiments have shown that vapour patterns are heavilyaffected by gravity, as qualitatively predicted. Notwithstanding this, nucleate boiling(see accompanying panel) is affected by gravity at low heat flux, where single-phaseconvection is still important, while it is largely insensitive to gravity at high heat fluxes(high vapour production). The same thing happens if an electric field is applied.Tentatively, a first conclusion can therefore be drawn: fully developed nucleate boilingis almost insensitive to gravitational and electric force fields. If further confirmation ofthis conclusion is found by future experiments, then a basic revision of the theory willbecome mandatory.


– Investigation of evaporation in porous media, developed in close collaboration withSabca and Prof. P. Stephan (Darmstadt University). The results could be used toimprove the working of capillary pumps in two-phase loops in microgravity.

– Testing of the performance of a two-phase loop by NLR (National AerospaceInstitute of The Netherlands).

– Detailed and fundamental study of the evaporation of a drop (Marseille University).– Evaporation inside a bubble (Marseille University).

The European Commission, via its Research Directorate, also supports the basic effortof this programme through a network called ‘ICOPAC’, which is co-ordinated by MRC(University of Brussels). This is just one example of the huge effort presentlydeveloping in order to answer very fundamental and basic questions that are of directinterest in industrial applications.

2.3.4.3 Low-Gravity Research into Boiling Phenomena

The overall heat-exchange performance of thermal equipment is commonly evaluatedby using the average value of the so-called ‘heat-transfer coefficient’, which is definedaccording to the Newton cooling law:

qα = (TW – TF)

where q is the power exchanged between the wall and the fluid per unit surface, andTw and TF are the wall and fluid temperatures, respectively. The various heat-transfermodes give very different (by several orders of magnitude) heat-transfer coefficientsand different achievable heat-flux values. For water this is summarised in the followingtable:

Table 2.3.4.1. The Heat-Transfer Coefficient for Water

The boiling process involves extremely complicated, non-linear physical processesthat operate over length scales ranging from 10 nm to 1 m or more. Strictly speaking,it is intrinsically a non-stationary process, although it shows a sort of ‘regularity’ on astatistical basis. This means that a sufficiently large number of bubbles must exist onthe heating surface, so that appropriate time and spatial averages of the phenomenon

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Heat-Transfer Mode Heat Flux Range (W/m2K)Free convection 100 – 1200

Forced convection in tubes 500 – 1200Nucleate boiling 2000 – 45 000

Filmwise condensation 4000 – 17 000Dropwise condensation 30 000 – 140 000

In general, the answer is as follows. Steady-state long-term nucleate pool boiling canbe attained in microgravity conditions. The possibility is higher with greatersubcooling and low heat fluxes. There is still debate about the possibility ofmaintaining that condition indefinitely and the role played by fluid properties and thesize and shape of the solid surface. At the present state of knowledge, it would beadvisable to keep the liquid at least slightly subcooled.

A further fundamental argument to be addressed concerns the value of the peak heatflux that is achievable. The mechanism leading to the peak heat flux (also termed‘burnout heat flux’, as it can even lead to physical destruction of the heater) is not yetwell-established. At least four mechanisms have been proposed. Tests in low gravitycould play a key role in the effort to achieve a much better understanding of thismatter. On the basis of the available results, it is known that this peak heat fluxdecreases with decreasing gravity. At the gravity levels usually available for low-g tests(g/g0 in the range 10-2 – 10-4) and for the size of the heaters tested, the mechanismleading to ‘burnout heat flux’ proved to be associated with vapour spreading on thesurface. Such behaviour was already suggested in the past, in accordance with therationale that gravity and heater size have a sort of interchangeable role. Thus ‘large’heaters become ‘small’ at low gravity, and vice-versa.

For large heaters (above a critical value), the proposed mechanism is the vapour/liquidinterface instability that proved to be the leading mechanism also for film boiling. Forsmall heaters, hydrodynamics no longer dominates the phenomenon and the vapour-front propagation mechanism comes into play. In this case, the effects of surfacetension and liquid and wall thermo-physical properties play a major role. Theapplication of an electric field increased both the peak and the film boiling heat fluxseveral fold, both on Earth and in low-gravity tests. The influence of the gravitationaland electric-field forces is briefly described below.

Few experimental studies on flow-boiling (see accompanying panel) in microgravityare reported in the open literature. Sub-cooled forced convective boiling was studiedin a 0.6 s drop-tower experiment. The phenomenon was found to have minimumreliance on gravity and is therefore considered to be a feasible and efficient heat-transfer mechanism in microgravity. An adequate velocity field is required to preventthe formation of vapour chunks, which tend to stick to the heater.

Heat transfer and two-phase flow have been investigated in a circular tube duringtransient quenching in parabolic flight. A thick vapour film on the tube wall, due to theabsence of gravity, made the re-wetting of the wall more difficult and degraded theheat transfer. Heat-transfer data on the flow boiling of water in a horizontal annuluswith a central heater rod during parabolic flight has been reported. Bubbles wereobserved to coalesce and move along the heater. The heat transfer was found to beinsensitive to the gravity level. Flow boiling of Freon-113 was also studied, using a


The following interpretation of this situation has been given. Nucleate boiling isdetermined by primary and secondary mechanisms. The primary mechanisms areindependent of gravity. They are determined by evaporation in the ‘micro-wedge’underneath the bubble and by capillary forces. The secondary mechanisms areresponsible for vapour transport: they are buoyancy, coalescence processes,momentum of bubble growth and formation, and thermo-capillary flow for subcooled states. The buoyancy can largely be replaced by the other secondary mechanisms inmicrogravity. Bubbles are definitely larger in microgravity. Furthermore, aphenomenon of lateral coalescence of bubbles along the heater surface has often beenobserved in low-gravity experiments, leading to a heat-exchange enhancement. This isin agreement with what has been found in Earth-based experiments. On the otherhand, it also means that fully developed nucleate boiling is a very effective heat-transfer mechanism also for space applications. This is very good news for spacethermal-device improvement, but the question arises of whether it is possible to keepboiling stable without buoyancy, i.e. without a force lifting bubbles away from theheating surface.

Pool and Flow Boiling

‘Pool boiling’ results when a still liquid in a vessel is heated to the boiling pointwithout any bulk liquid motion. Carefully watching the fluid during the heatingup process, it is easy to recognise different ‘boiling regimes’. At first a few bubblesare seen (in vertical columns) stemming from the heated surface of the vessel.This is usually called the ‘regime of single bubbles’. Once the power supplied tothe liquid increases, the number of bubbles greatly increases, together with theagitation in the liquid. This corresponds to the ‘fully developed nucleate boiling’regime, or simply ‘nucleate boiling’. If a similar process takes place in a tube witha bulk motion of the fluid, it is referred to as ‘flow (or forced-convection) boiling’.

It is commonly said that water boils at 100ºC. More appropriately, it should besaid that water, at atmospheric pressure and 100ºC, is saturated. Thus, if theheated surface (e.g. of the above vessel) is taken to a little higher temperature,bubbles form on it and move off into the fluid. This is usually called ‘saturatedboiling’. But bubbles (and thus boiling) can exist at the heated surface also if thewater temperature is below 100ºC, provided that sufficient power is supplied tothe fluid. In this case, the bubbles can start condensing even in the vicinity of thesurface, and no bubbles can be detected within the liquid pool. This situation istermed ‘subcooled boiling’.


vertical tube internally coated with a gold film, in parabolic flight. The verticalorientation allowed the examination of the effect of various gravity levels during theflight parabola, with no flow transition. Bubbly, slug and annular flow regimes wereexamined. As usual, large variations in bubble and slug sizes with gravity level wereobserved.

The heat-transfer coefficient was found to be insensitive to the gravity level, with theremarkable exception of annular flow, where boiling is suppressed in the liquid layer.In that case, due to the increase in film thickness and the reduction in turbulence, theheat transfer was degraded in microgravity and enhanced in the subsequent high-gphase of the parabola. It was concluded that, provided boiling is not suppressed atthe surface, heat transfer is quite unaffected by the gravity level. Further studies areneeded to investigate this boiling transition. Due to the limited amount of workperformed so far, it is very difficult to draw definite conclusions on forced convectiveboiling.

The great importance of this subject has been widely recognised in the recent past bythe international research community in this field. As a consequence of this, a TopicalTeam on Boiling has been established by ESA, composed of European scientists andcertain industrial representatives, including Alenia Spazio and DASA. A further MAPproject is in progress on boiling, led by LOTHAR (LOw gravity and Thermal AdvancedResearch laboratory) at the University of Pisa. Last but not least, an InternationalWorking Group on boiling and two-phase flow, involving members from Canada,France, Germany, Italy, Japan and the USA, is operating to facilitate joint futureactivities to be performed on the International Space Station. This group is itself afurther confirmation of the need for scientific co-operation between boiling (pool andforced convective) and two-phase-flow specialists.

- Force Fields Play with Bubbles

Anyone who shakes a bottle of mineral water can watch either vapour or gas bubblesflowing towards the liquid free-surface, due to buoyancy. What could one expect to seeif living on a planet with a different gravity level, or on an orbiting platform like theInternational Space Station?

Figure 2.3.4.2 can help to provide some answers. The pictures were taken during aboiling experiment with a wire (0.2 mm in diameter), all with the same wall heat fluxand with a small liquid sub-cooling. The first three pictures refer to the effect of the(equivalent) gravity acceleration. At 1g, as in (a), all bubbles detach from the wall andrise upwards. If the gravitational force is doubled (b), the bubbles behave in the sameway, but their size is smaller as they detach earlier from the wall, thanks to thedoubling of the buoyancy force. If the acceleration vanishes, the lifting buoyancy forcevanishes as well, leaving surface tension to bind the bubbles to the wall. Thus, if no

222 sdddd SP-1251

Figure 2.3.4.2. Bubble size and number as afunction of gravitational and electric forces: (a) g/g0 + 1; 0 kV (b) g/g0 = 2; 0 kV (c) g/g0 =0.02; 0 kV (d) g/g0 = 1; 10 kV (e) g/g0 = 0.02;10 kV

other buoyant forces are present, bubbles grow at the wall to a bigger size withoutdetaching as in (c), where the residual acceleration is 10–2g. The bubbles are seen to bemuch larger and tend to accumulate close to the wall and coalesce. Their bulk flow isstill directed upwards, but this is only due to a residual acceleration in the oppositedirection.

A quite different vapour pattern is shown in the other two photographs, where onlyvery tiny bubbles can be observed, spreading in almost any direction in the directproximity of the heating wire. Picture (d) refers to a 1g situation, whilst picture (e) refersto the same low-gravity level as before. How can we obtain such an effect?

(a)

(b)

(c)

(d)

(e)

REFERENCE FLUID HEATER NOTES

Snyder & Chung , 2000 PB DT FC72 Flat plate: 25x25 mm Electrostatic field applied, 2 s duration

Di Marco & 1997 PB PF R113 Wire: 0.2 mm diameter With and withoutGrassi 1998 SR FC72 applying electrostatic

1999 PF FC72 field2000 GB SR FC72 Cylinder: 1 mm diameter

DTStraub and 1984 PB SR R113 Flat plate: 20x40 mm Saturated andcoworkers subcooled conditions

1992 PF R12 Wires: 0.2, 0.05 mmdiameter. 40x20 mmflat plate

1996 SR R113 Wire: 0.2 mm diameter1999 OF R134a Wires: 0.2, 0.05 mm

diameter1998 OF R123 1.4 mm diameter1999 hemispherical heater

Suzuki et al., 1999 PB PF Water Ribbon: 0.1mm thick, Subcooled conditions20x5 mm CHF only

Motoya et al., 1999 PB DT Water Wire: 0.2 mm diameter Effect of scale foulingLee et al., 1997, 1998 PB OF R113 Flat plate: 19x38 mm Different subcooling

tested. Low heat flux(up to 80 kW/m2 )

Oka et al., 1996 PB DT Water and Flat square plate: 30,R113 40 and 80 mm

Tokura et al., 1995 PB DT Methanol WiresOka et al., 1994 PB DT Water–

ethanol mixOka et al., 1992 PB PF R113, pentane Flat plate Several flights

water performedMerte, 1990 PB DT Liquid nitrogen Disc, upward and

downward facing andvertical

Siegel, 1965 PB DT Water, alcohol, Wire: 0.5 mm diameter,60% sucrose horizontal and verticalsolution

Kawaji et al. 1991 CB PF R113 Circular tube Quenching experimentsOhta et al., 1992 CB PF R113 Vertical tubeSaito et al. 1992 CB PF Water Annulus with inner rodWang et al., 1995 CB DT R113 Flat plate: 25x25 mm 0.6 s free fall, 0.003 g


Legend:OF = orbital flight; SR = sounding rocket; PF = parabolic flight; DT = drop tower/shaft.PB = pool boiling, CB = convective flow boiling, GB = gas bubbling

The answer looks obvious: by introducing a force field other than gravity. In fact, thosefinal patterns were obtained by imposing a radial electric field (the wire is the innerelectrode of something similar to a cylindrical electric condenser). Due to thedifference between the electrical permittivity of the vapour and liquid and to thepresence of electric-field gradients, a net force arises that pushes bubbles (smallerpermittivity) towards regions with a weaker field. Liquid drops in a gas wouldexperience just such an opposite force, which would enhance vapour condensation onthe wall. If the field is high enough (as in these photographs), the effect of gravity isalmost negligible. The electric field proved to be a good means for enhancing heattransfer both on Earth and in low-gravity conditions, and could be a useful means ofperforming fluid management in space.

2.3.4.4 Conclusion

It is evident that low-gravity experiments are making important contributions to theunderstanding of the physics of boiling, of heat transfer and of diffusion, and that theirpotential value for improving the efficiency of industrial processes is very significant.But what should be done in the future? The past activity in low gravity has beenfragmentary, as is clearly shown in Table 2.3.4.2. This has been due to some lack of co-ordination, to the large variety of low-gravity platforms, and to the time required forthe assessment of any complex scientific process.

The set of available facilities for such low-gravity experiments is very wide. It rangesfrom drop towers and drop shafts (experiment duration for each shot, 5 to 10 sec) toorbiting platforms (days). The various facilities have different characteristics in termsof available volume, power, energy, support hardware and software. Thus eachexperiment has to be conceived taking due account of these constraints. This situation can make it difficult to compare results originating from different types offacilities that were used under quite different low gravity regimes.

The International Space Station will therefore provide a unique and welcomeopportunity to reasonably relax most of these constraints. It will allow the repetitionof measurements under the same conditions and in the same instrument, which iscrucial. In addition, the long duration of the tests will ensure the achievement ofcontrolled and steady conditions. The recent Call for Experiments issued by ESA showedthat there is strong interest on the part of the scientific community and of industry ininvestigating applied problems. This should be managed through Topical Teams.

Table 2.3.4.2. Overview of boiling experiments in microgravity

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Acknowledgements

We would like to thank Prof. G. Frohberg (TU Berlin, D), Prof. L.P.B.M. Jansssen (Univ.Groningen, NL) and Dr. C. Colin (Institut de Mécaniques des Fluides, Toulouse, F) forhelpful information, discussions and comments.

Further Reading

Frohberg G., Kraatz K.H., Wever H., Lodding A. & Odelius H. 1989, Diffusion in liquidalloys under microgravity, Defect and Diffusion Forum, 66-69, p. 295.

Kuhlmann H.C. 1999, Thermocapillary Convection in Models of Crystal Growth,Springer Verlag.

Legros J.C., Van Vaerenbergh S., Decroly Y., Colinet P. & Montel F. 1994, Microgravityexperiments studying Soret effect: SCM, SCCO, MBIS, Entropie, 184, p. 44.

McQuillen J., Colin C. & Fabre J. 1998, Ground-based gas–liquid flow research inmicrogravity conditions: State of knowledge, Space Forum, 3, p. 165.

Van Oost S., Dubois M. & Bekaert G. 1995, Test results of reliable and very highcapillary multievaporators/condenser loop, Proc 25th Int. Conf. on EnvironmentalSystems, San Diego (SAE 951506).

Walter H.U. 1987, Fluid Sciences and Materials Science in Space, Springer Verlag.

2.3.5 Critical-Point Phenomena

D. Beysens


The transition between the vapour and liquid phases of a pure fluid is one of the mostfundamental in nature. The reference point, from which all of the transition propertiesof such a fluid can be derived, is called the ‘critical point’. This is the point,characterised by a fixed temperature, pressure and density, at which the distinctionbetween the gas and the liquid phase simply disappears. It was the French baronCharles Cagniard de La Tour, in 1821, who first discovered this critical point, observingthe disappearance of the gas/liquid interface of carbon dioxide in a sealed gun. Hecould not know, at that time, that this new ‘state’ of matter would lead later on to somany important discoveries for both fundamental science and technology, some ofthem thanks to exploiting the microgravity environment.

The critical point of carbon dioxide (CO2) occurs, in fact, at 31˚C and at a pressure of72 bar (atmospheres). That of water (H2O) is observed at 375˚C and 225 bar, and thatof hydrogen at 33 K and 13 bar.

In a wide domain around the critical point, important parameters such as isothermalcompressibility, the density of the gas and liquid phases, and the surface tension, obeyuniversal power laws. Theseparameters can easily bevaried by using small changesin the temperature. The highlyvariable properties of near-critical fluids make them veryappealing for studying manyinteresting phenomena that,because of the universality ofthe power laws, are valid for all


Figure 2.3.5.1. Phase diagram of apure substance in the

temperature/pressure plane. Thesupercritical ‘state’ corresponds to

a compressed gas that exhibits thedensity of a liquid

universality’. This class is defined by the space dimensionality d (=3 in normal space)and the dimensionality n, of the fluctuating quantity, the ‘order parameter’. This is theparameter (M) that describes the change in the symmetry of the system at thetransition. In fluid systems, the order parameter M is the density.

Density is homogeneous above the critical point (the fluid is supercritical) andinhomogeneous below it, because the two phases (gas and liquid) coexist withdifferent densities. All systems with the same ‘d’ and same ‘n’ show the sameasymptotic, universal, scaled behaviour. They all belong to the same ‘universalityclass’. Fluids belong to the class defined by d=3, n=1 (density is a scalar). In additionto pure fluids (order parameter: density), another member of this same class are thepartially miscible liquid mixtures (order parameter: concentration). This includes thepolymer melts, polymer solutions, micro-emulsions, molten salts, and monotecticliquid metals. Many other non-fluid systems also belong to this class, including themagnetic 3d Ising model (order parameter: magnetisation), which is relatively easy tostudy theoretically and is often considered a good representative of this class. Anexample of another class is He4 near its λ point, which belongs to the class d=3, n=2,where the order parameter, a wave function, is a 2D vector. This universality andscaling is fundamental in nature. It stems from the universal behaviour that the freeenergy must asymptotically obey at the critical point in order to fulfil the conditionsof a second-order phase transition. (In such a transition, a specific property changescontinuously, rather than discontinuously, on going through the transition). In thissense, universality and scaling are generic to all critical-point phenomena.

By permitting measurements extremely close to the critical point, space experimentshave made possible the precise measurements of important, weak power lawdivergence, such as that of the specific heat at constant volume Cv (Fig. 2.3.5.2). Forexample, from space experiments, the temperature divergence of the specific heat hasbeen determined with a very high precision.

With the reduced temperatureε = T – Tc / Tc (where T is temperature and Tc is thecritical temperature), the specif-ic heat diverges as Cv~ ε−α nearthe critical point. The ‘critical’exponent α is universal. Itsprecise determination was a key


fluids. Above the critical temperature and pressure, such fluids are called‘supercritical’. In this region, they exhibit a number of specific properties (high density,low viscosity, large diffusivity), which make them intermediate between liquids andgases. In addition, their isothermal compressibility can become extremely large,especially when they approach the critical point.

Fluids in their supercritical state are increasingly used by the food and waste-management industries for their solubilisation properties (e.g. supercritical CO2), ashosts for ‘cold’ combustion (e.g. supercritical water), in energetics (supercriticalthermal or nuclear plants), and in astronautics (e.g. storage of cryogenic fluids).However, their behaviour under both terrestrial (1g) and space (0g) conditions is notwell known. Consequently, their current use without such knowledge inevitably raisesfundamental questions concerning fluid dynamics, heat transfer, interfacialphenomena and chemical processes. Experimentation on the International SpaceStation (ISS) is therefore a tremendous opportunity to address these questions and toenhance knowledge in this field, which is of both fundamental and industrial interest.

Fluids in their near-critical or supercritical state are affected by gravity. At the criticalpoint, the compressibility of the fluid is actually infinite and when approaching it isvery large. Consequently, gravity compresses the fluid under its own weight and thefluid stratifies. This prevents a very close approach to the critical point. Anymeasurements made on a cell of finite height will actually measure an averagedproperty of the fluid at differing densities, rather than the precise propertyapproaching the critical point.

Experimentation in microgravity is not only of value in avoiding the complications dueto compression. It also has value because convection and buoyancy are absent. Close to the critical point, fluids exhibit anomalies in the transport of heat. Due togravity-driven convection and buoyancy phenomena, often turbulent, appear for evenminute temperature gradients. In the following, it is shown that experimentation inmicrogravity has enabled new phenomena to be discovered, thanks to the ability toachieve a close approach to the critical point and the removal of convection andbuoyancy. The main characteristics of fluids in the vicinity of their critical point arepresented, together with the highlights of previous space experiments. Finally, there isa discussion of the main topics to be addressed in critical-point research using the ISS.

2.3.5.2 Power Laws and Universality

An important aspect of the critical region is that most of the anomalies in thethermodynamic and transport properties can be set in the form of scaled, universalfunctions (power laws) with respect to the critical-point parameters. This has the veryimportant consequence that any results obtained with one fluid can be immediatelyre-scaled to describe any member of a whole class of systems, called a ‘class of

228 sdddd SP-1251

Figure 2.3.5.2. Critical anomaly inthe specific heat at constant volume

(Cv) measured under 0g in SF6(Spacelab-D2, 1993)(from Haupt andStraub 1999, Phys. Rev. E9, p. 1795) T - Tc, K

C v, J

/Mol

k

correlations. That involves the dimensionality of the physical space d, and thedimensionality n of the fluctuating quantity, the order parameter M. These are theonly relevant attributes of the system when in this condition. As outlined above, theprincipal of universality then classifies diverse physical systems according to thevalues of d and n, with all systems of the same class displaying the samethermodynamic behaviour.

2.3.5.4 Time Scales

The scaling laws defined for systems in thermodynamic equilibrium are often called‘static scaling laws’. It is, however, possible also to define universal dynamic scalinglaws for the transport coefficients. The dynamics of the density (more generally, orderparameter) fluctuations appear to define the natural time scale, much like thecorrelation length ξ defines the natural length scale for the spatial fluctuations. Thisnatural time scale is the decay time of a fluctuation of size ξ over the length scale ξSuch a fluctuation vanishes by a (thermal) diffusion process, with a diffusioncoefficient that can be estimated from the Brownian diffusion of a cluster of size ξ. Thetypical time tξ diverges near the critical point. It follows that the density fluctuations(or order parameter fluctuations) relax more and more slowly as the systemapproaches its critical point. This is the phenomenon of ‘critical slowing-down’.

In a fluid, pressure equilibrates nearly instantaneously (in fact, at the velocity ofsound), so that both density and temperature fluctuations are slowed down. Inparticular, the thermal diffusivity tends to zero and the time to equilibrate thetemperature also diverges. As a practical matter, the time for achieving thermalequilibration can become very long. For example, in the absence of convection(microgravity environment), the time to reach thermal equilibrium, at a temperaturewhich is 1 mK from Tc, for a CO2 sample with thickness 1 cm, would be more than amonth.

Once properly scaled by ξ, the natural length-scale of critical-point phenomena, andtξ, the fluctuation lifetime, many phenomena are universal. Thus the critical pointenables a zoom (ξ) and a slow-down (tξ) of the phenomena to be studied. Rescaling alllengths by ξ and the evolution times by tξ, enables the fluid behaviour to be cast onsingle, universal master curves.

2.3.5.5 The ‘Piston Effect’

Classically, there are three modes for thermalisation to take place: radiation, diffusionand convection. However, in very compressible fluids like near-critical fluids, anotherthermalisation effect, the ‘piston effect’, is dominant. This thermalisation mechanism– discovered in microgravity experiments – originates from the high compressibilityand expandability of a supercritical fluid.


test of the ‘Renormalisation Group’ theory, which has been developed to try toimprove on the classical macroscopic description of fluid behaviour close to thecritical point. The value deduced from the space experiments, α = 0.1105 + 0.025/–0.027, indeed appears to be very close to the result of the Renormalisation Grouptheory, α = 0.110 ± 0.005.

2.3.5.3 The Correlation Length of Fluctuations

As the critical point is approached, the fluids become extremely compressible, muchmore so than ideal gases. Excited by the thermal fluctuations and enhanced by thelarge compressibility of the fluid, the density fluctuates more and more strongly as thecritical point is approached. The vicinity of the critical point is thus characterised bythe presence of very-large-scale density fluctuations (or more generally, orderparameter fluctuations), which develop throughout the fluid. The density fluctuationsgive rise to unusually strong light scattering, the so-called ‘critical opalescence’. Theseorder parameter fluctuations are correlated with the correlations having a spatialextent that can be characterised by a correlation length ξ. The specific nature of thecritical region therefore involves the appearance of this new characteristic distance,which can become much larger than the inter-particle distance. The correlation lengththen becomes the natural length scale of critical-point phenomena.

At that point where the correlation length becomes much larger than the range of theintermolecular forces, the specifics of the microscopic interactions cease to be relevantin the description of the critical behaviour. All that matters is the structure of the

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Figure 2.3.5.3. Huge density fluctuations as observed under 0g in SF6 (Mir, 1996; T – Tc =10 µK). Fluctuations in density diverge at the critical point and their typical size, the‘correlation length ξ’, determines the length scale of all critical-point phenomena

2.3.5.6 Phase-Separation Dynamics

Although phase separation in fluids and liquid mixtures is a common process thatoccurs in many areas of science and technology, the connection between themorphology of domains and the growth laws is still incomplete. A typical phase-separation experiment consists of quenching the temperature of a sample at thehighest possible rate from an initial state (density ρ, temperature Ti) where it ishomogeneous to another state (density ρ, temperature Tf). In this latter state, thesample is no longer stable and the process of phase separation occurs (Fig. 2.3.5.6). Inthe critical region, it is easy to vary continuously the physical parameters. Inparticular, the temperature quench depth is related to the equilibrium volume fractionφ of the minority phase, so that φ may be varied.

As discussed above, the ‘piston effect’ speeds up thermalisation (at the cost of a thinboundary layer) so that thermal quenches very close to Tc are limited only by thethermal response of the thermostat. The critical slowing down is, however, stilleffective in the droplet growth process and enables a detailed investigation of themechanisms involved in the separation process.


The basic physical mechanisms giving rise to the piston effect are the following (Fig. 2.3.5.4). When a homogeneous bulk fluid enclosed in a sample cell is suddenlyheated from one wall, a diffusive thermal boundary fluid layer forms at the wall/fluidinterface. Due to the high thermal expansion of the fluid layer and the highcompressibility of the bulk, the fluid layer expands and acts as a piston toadiabatically heat the fluid. As a result, a spatially uniform heating of the bulk fluid isproduced.

The characteristic time scale for the piston effect is the time tc to transfer from theboundary layer (thickness δ) the amount of energy that adiabatically heats theremaining fluid. In contrast to the diffusion time tD that diverges near the critical point,this time tends to zero with the increase in compressibility of the fluid. A striking resultof this analysis is the critical speeding up of the piston effect when getting closer to thecritical point. As a matter of fact, near the critical point, tc goes to zero although tDgoes to infinity. This result represents an enormous reduction in the time required forthermalisation. This reduction is obtained at the cost of the formation of a boundarylayer that diffuses slowly so that the ultimate equilibration time in pressure,temperature and density still remains the diffusion time-scale.

An additional result shows that the fluid velocity produced by the expansion of the hotboundary layer reaches its maximum value at the edge of the layer. The edge fluidvelocity induces the compression of the bulk fluid by a small transfer of matter andmakes the boundary layer act as a converter that transforms thermal energy intokinetic energy. This transformation is at the origin of a very particular behaviour whenthe vapour is in equilibrium with liquid below the critical point (Fig. 2.3.5.5). Whileheating the cell, the temperature of the vapour becomes greater than that of the wall,apparently violating the Second Law of Thermodynamics.

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Figure 2.3.5.4. The ‘pistoneffect’ mechanism: a thin hotboundary layer expands andcompresses the bulk fluid. Thecorresponding temperatureprofile exhibits a thin zone ofstrong gradients near theheated boundary (thermalboundary layer δ), and ahomogeneous rise in the restof the fluid, which settles atthe speed of sound

Figure 2.3.5.5. Overheating of nearly 20% in the gas phase of a SF6 sample at 10 K belowthe critical point (ALICE on Mir in 1999). A temperature rise of δ Tw = 0.1 K is imposed atthe cell wall. The temperature evolution of the gas (δ TG) and that of the liquid at two

locations (δ TL1,2) are shown. In the insert, the sample with the thermistors is shown (from

Wunenburger et al. 2000, Phys.Rev.Lett, 84, 4100).

The existence of the twodifferent regimes, theirrelation to the patternmorphology and the absenceof a crossover can beexplained as an interplay between the droplet coalescence, as induced by Browniandiffusion, and the hydrodynamics interactions as induced by the coalescence processitself. The transition between the two regimes appears at a well-defined volumefraction, of order 30%.

2.3.5.7 Critical Enhancement of Adsorption

The behaviour of pure fluids and fluid mixtures near a plane wall, which can beconsidered as a third phase, is also strongly modified by the proximity of a criticalpoint. In particular, in the one-phase region, the adsorption of fluid moleculesproduces a density variation that scales with the correlation length in a universal,critical adsorption profile. With z the perpendicular distance to the wall, the densityvaries as ρ (z) ~z1/2 , at distances z < ξ and ρ(z) ~exp(-z/ξ) at z >ξ.

Gravity-free experiments, to take advantage of a bulk sample at uniform density, wereperformed with SF6 adsorbed on black carbon (a porous material to increase thesurface of adsorption). The expected increase in adsorption was measured, as shownin Figure 2.3.5.8. However, when the temperature at which the correlation length ofthe fluctuations became of the order of the pore size was reached, the phenomenon of‘critical desorption’ was observed instead! The finite size of the pores, by limiting thesize of the fluctuations, ‘killed’ the critical character of the fluids and suppressed theexcess adsorption caused by the approach of the critical point.


The typical scenario for theformation of a new phase doesnot correspond to the twoclassical processes of ‘nucleation’or ‘spinodal decomposition’. Inclassical nucleation, only largefluctuations can overcome theenergy cost corresponding to theformation of the interface of a nucleus of the new phase. In spinodal decomposition,fluctuations are unstable and grow. Near the critical point, the large fluctuations in theorder parameter induce another process called ‘generalised nucleation’. In this process,the large order parameter (density) fluctuations of average size ξ grow in amplitude toreach local equilibrium and give rise to droplets of the minority phase. These dropletsthen grow at the expense of the majority phase, until they reach equilibrium.

Experiments that are free of gravity effects have shown the key role of the coalescencebetween drops, either by Brownian motion or local flows induced by the coalescenceprocess itself. At very small volume fractions, these interactions should be very rare.Only a diffusive process should take place. However, recent experiments seem to showthat, even at very low volume fractions, hydrodynamics still plays a key role.

When the density of the fluid is critical, i.e. when the volumes of vapour and liquid areequal (φ = 1/2), an interconnected pattern of domains that coalesce continuously isformed (Fig. 2.3.5.7a). The characteristic length Lm of the domains can be defined asthe pseudo-period between the phases. At late times, Lm ~ t. The results obtained inall fluids and liquid mixtures, when rescaled by the unit of length (ξ) and time (tξ) asKm* = 2 πξ / Lm and t* = t/tξ can be reasonably placed on the same master curve,which obeys scaling and thus strongly suggests universality.

When the volume fraction of the domains is smaller (Fig. 2.3.5.7b), and the gravityeffects are negligible, the droplets coalesce and/or grow by Brownian motion.Experiments show that the late stages are always characterised by a 1/3-growth-lawexponent. All the data obtained in liquid mixtures and in fluids during the gravity-freeexperiments, when expressed in the scaled units Km* and t*, can be placed on thesame master curve Km = 0.9 t*1/3, making clear the universality of phase separationin fluids and liquid mixtures.

234 sdddd SP-1251

Figure 2.3.5.6. Schematic phasediagram for simple fluids and liquid

mixtures in the T – M plane. T istemperature and M is the order

parameter (M = ρ – ρc / ρc for simplefluids, and M = c – cc for liquid

mixtures)

Figure 2.3.5.7. Growth laws influids (SF6, CO2, data points) and

liquid mixtures (partiallydeuterated cyclohexane and

methanol, letters and squares)when gravity effects are absent

(from Beysens et al., Proc. 8thTohwa Intl. Symp. on Slow

Dynamics in Complex Sysems,November 1998)

This programme, which could extend over about a decade, contains elements that aredirected both towards fundamental studies and at industrial applications.

- A New Hydrodynamics?

For static phenomena, fluids and liquid mixtures belong to the universality classdefined by an ideal magnet (the 3D Ising model). In this model, flows and moregenerally hydrodynamics are not present. However, hydrodynamics often inducesunexpected behaviour in those fluids, especially in heat- and mass-transport phenomena,by convective flows. This occurs even in the absence of gravity. In particular, forsupercritical fluids, which are as dense as liquids and more compressible than gases,it is a ‘novel’ hydrodynamics that has to be considered. This is a developing area andone that will certainly lead to new and unexpected results in the future.

- Direct Observation of Critical Fluctuations

The first documented observation by Andrews, in 1869, of critical opalescence in apure fluid near the critical point was cited as the evidence for large-scale densityfluctuations. Although there is much evidence for the existence of critical fluctuations,only a few attempts have been made, including recent experiments on Mir, to observeand analyse fluctuations directly. Future low-g experiments plan to image and studycritical fluctuations, both in volume and time, in considerable detail.

Optical measurements within pressurised cells allow the direct observation of suchcritical fluctuations. Data from within 10 µK of the critical point can be obtained.There, critical fluctuations with a correlation length as large as 15 µm should beobserved. A detailed study of the distribution of the fluctuations will allow valuablenew information to be gathered. This would include such aspects as the fractaldimension of the fluctuation pattern, the statistics of fluctuations and the expecteddeviation from Gaussian statistics related to the universal form of the free energy. Allof these quantities are fundamental in probing the universal character of the critical point.

- Phase Ordering

Knowledge of the mixing and separation of substances has been important to humancivilisation for thousands of years. Research into this process of ‘Phase Ordering’ hasbeen particularly active in recent times, partially motivated by the need for bettermaterials. Phase separation in liquid mixtures and pure fluids is a natural phase-ordering process, and occurs in many areas of natural science, engineering andindustry. Moreover, engineering applications are especially important in the two-phaseheat- and mass-transfer processes that are used in many industries. Phase separationis also ubiquitous in materials processing for, for example, metallic alloys, polymer alloys,including supercritical elaboration of materials, and flat-panel display technology.


2.3.5.8 Critical Boiling

When a two-phase fluid is heated, boiling often occurs. When the heat flux is very strong,vapour can spread onto the heater. This is the so-called ‘boiling crisis’, which can havecatastrophic consequences in thermal and nuclear plants, since as a vapour filmdevelops on the heater it prevents heat transfer. Near the critical point, the vapour-liquidinterfacial tension σ goes to zero as σ ~εν. Under zero gravity and near the critical point(where σ is very small), phenomena that are important only at small scale and high heatflux become visible. In fact, the spreading of the dry spot of a bubble vapour has beenobserved under 0g and it is interpreted as the precursor of the boiling crisis. Spreadingoccurs under the influence of a recoil force, or a ‘thrust’, produced by evaporating liquidnear the liquid/solid/vapour contact line. When heating the two-phase fluid, the vapourbubble is seen to spread on the cell walls (Fig. 2.3.5.9).

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Figure 2.3.5.8. Adsorption excess(arbitrary units) near the critical point

of a fluid (SF6) on a porous material(Vulcan 3-G graphitised carbon black)

under 0g (on Eureca-1 in 1992).Although the general increase in

adsorption is clearly observed whentemperature T decreases towards the

critical temperature Tc, when thetemperature T is very close to Tc a

paradoxical decrease in adsorptionoccurs (from Thommes et al.1994,

Materials and Fluids in Low Gravity, Springer, p. 51)

Figure 2.3.5.9. Critical boiling andout-of-equilibrium wetting undermicrogravity (SF6, Mir, 1999). Gasapparently ‘wets’ the wall duringheating (a – d). This sequence wastaken during a temperaturequench from Tc – 0.2 K (a) to Tc – 0.1 K (d). (a) t = 0; (b) t = 11 s; (c) t = 17 s; (d) t = 37 s (from Garrabos et al., J. Chim.Phys.,96, 1066)

2.3.5.9 An Experiment Programme for the ISS

The following is an outline of a possible programme of experimentation in thisfield, following the recommendations and proposals of the members of theTopical Team for ‘Chemical Physics in Near-Critical and Supercritical Fluids’.

boiling crisis in industrial heat exchangers, it is therefore likely that such experimentswill provide new insight into the understanding of this problem. In addition, theserecently observed and unexpected results on the interface dynamics open a new fieldfor investigating boiling and two-phase thermalisation by the piston effect.

- Supercritical Solubilisation

Fluid systems in the near-critical and supercritical state have a great affinity to dissolvegas, liquid or solid material of other substances. One of the first commercialapplications of this phenomenon (in the 1980s) was the decaffination of green coffee.At present, CO2 extraction processing of coffee is one of the most importantapplications of supercritical fluids. Another classical application is the treatment oftobacco with supercritical CO2 or nitrogen. Such treated tobacco contains much lessnicotine and the tar condenses when it burns.

A growing interest in supercritical fluids as a reaction medium is also documented inrecent literature. Contaminated and poisonous substances can be oxidised andneutralised in supercritical H2O, or in other supercritical liquids. At present,supercritical fluid processing is achieving greater acceptance in the chemical,petroleum, and food industries. Critical fluids can be used as solvents and reactionmediums with specific properties in terms of density, pressure, and temperature,allowing their application for various purposes. For instance, a variety of substanceswith different critical parameters are licensed for unlimited use in food treatment.

Although supercritical fluid processing has gained increasing acceptance in manytechnical applications, the underlying physics is still not really understood. Openquestions include: Why are critical fluids such excellent solvents and reactionmediums, and what is the process of mass transport in these fluids? Thisunderstanding of its physical nature is necessary for future progress. The solubility ofa critical and supercritical fluid is caused by strong density fluctuations, related to thehigh compressibility of the fluid. This results in local microscopic inhomogeneities indensity. One may picture it as ‘a dynamic liquid zeolite’. Thus it has a ‘porous’structure, similar to that of a zeolite, with similar attractive forces to adsorb othersubstances within the pores. It is therefore proposed to undertake basic studies ofcritical fluids, in terms of dimensionless parameters for temperature and density,specifying the distance to the critical point. These would cover the basic nature of thesolubility, the mass transport by means of mass diffusion, and the kinetics of theinterface mass transport.

- Supercritical Water Oxidation

Oxidation in a supercritical water reactor is a powerful tool for transforming complexand dangerous organic compound wastes into their simple constituent components


Most of the key experiments in this field have been performed near the critical pointof binary liquid mixtures or pure fluids, which provides scaling and, thanks to thecritical slowing down, allows the hydrodynamics of coalescence to be observed andmeasured. The results from such phase-separation experiments have shown that thelate stages of phase separation are universal, i.e. the growth laws are described bymaster curves that are valid for all fluids, within two scale factors. The theoreticalstudy of the late stages of this process has included the use of generic concepts suchas scaling and self-similarity, universality, and hydrodynamic percolation.

The accumulation of data under microgravity shows, however, that the behaviour ofsuch fluids, although similar to that observed with liquid mixtures, exhibits a numberof significant differences. To understand them, a refined analysis of the localhydrodynamics (at the scale of the domain size) is needed to take into account allpossible sources of discrepancy (thermal piston effect, fluctuation effects, turbulentand inertial effects, Brownian motion, etc.). The fluctuation or noise effect (Brownianmotion) in hydrodynamics has not been taken into account yet. There is a need togather data and analyse the growth at very low volume fractions. A new developmentconcerns the investigation of phase transitions induced by mechanical quenches, byusing a volume (or density) variation. This is a new way to induce phase ordering, incontrast to the temperature quenches that have hitherto been used.

- Boiling, Two-phase Thermalisation and Wetting

A process that is complementary to phase separation (one-phase to two-phases) isboiling (two-phases to one-phase). Boiling in liquid mixtures and pure fluids, like phaseseparation, is a common process that occurs in many areas of natural science,engineering, and industry. The engineering applications (e.g. supercritical waterthermal plants) are especially important in the context of industrial heat-transferprocesses. A clearer understanding of the exact physics of boiling is therefore desirableboth for improving industrial efficiency and in developing new products. The region inthe vicinity of a critical point, under weightlessness, is particularly interesting becauseit permits a clear observation to be performed thanks to the critical slowing-down andthe absence of buoyancy.

Below Tc, the vapour phase co-exists, under low-g conditions, with the liquid phase asa bubble, and the liquid wets the cell wall. However, when boiling occurs, the vapourphase appears to ‘wet’ a large portion of the solid surface and large temperaturegradients are measured between the gas and liquid phases. These gradients are relatedto the two-phase character of the adiabatic fluid heating (diphasic piston effect).Preliminary analyses seem to confirm that the surface-tension gradients are not themain cause. The vapour recoil force, due to momentum transfer at the interface duringevaporation, shows a large divergence as T tends to Tc and thus appears as the mostprobable cause. As the recoil force is suspected to be the cause of the well-known

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2.3.6 Interfaces, Foams and Emulsions

A. Passerone & D. Weaire

2.3.6.1 Surface Tension

Surface tension is a basic property of all liquid surfaces and interfaces. It expresses theresistance of an interface to stretching. Many manifestations of surface tension andthis resistance to stretching can be found in everyday life. For example, a water surfacecan support small objects, a thin liquid layer tends to form droplets rather than tospread on a solid surface, and liquid drops that hang from taps and soap bubbles arealmost perfectly spherical.

Indeed any liquid interface acts more or less as a stretched elastic membrane, so thata force is exerted between the two sides of any imaginary line on the surface or alongthe contact line between a liquid interface and a solid. Hence water can support anobject provided that the force exerted by the surface tension along the contact line islarger than the object’s weight. A drop can hang in equilibrium if its weight is smallerthan the surface-tension force exerted along the contact line with the solid support.

Surface (or interfacial) tension σ is the force per unit length needed to keep an interfacecut along a line in mechanical equilibrium, as illustrated in Figure 2.3.6.1.

As a direct consequence of the existence of the interfacial tension, there is a differenceof pressure across any curved liquid interfaces, called ‘capillary pressure’. Forexample, there is a larger pressure inside a droplet than outside. Like a balloon that isstretched by the internal over-pressure, a soap bubble is kept fromcollapsing by this capillary pressure.

The existence of this pressure wasfirst recognised by Laplace and byYoung at the beginning of nineteenthcentury. The relationship between


(CO2, H2O and minerals). In addition, these reactors operate at moderate temperatures(about 400˚C) and pressures (about 500 bar) in a process that is harmless to theenvironment. The yields of these oxidation processes are extremely high. Theirmechanisms and dynamics involve heat and mass transport by diffusion, convectionand possibly thermo-compressible effects associated with the adiabatic piston effect.

Because supercritical water breaks down dangerous organic molecules so effectivelyinto simple and safe byproducts at relatively low pressures and temperatures,chemical reactions in supercritical water, sometimes called ‘cold combustion’, are ofconsiderable interest to industry. These reactions need very strong convection to mixthe reactants. Present and future developments in supercritical reactors, supercriticalheat exchangers, and more generally supercritical pilot plants, depend on the waygravity effects are taken into account.

There has been no previous gravity-free investigation of combustion phenomena insupercritical fluids. Here chemical reaction (oxidation) must couple with thermo-compressible effects, like adiabatic heating by the Piston Effect. Experiments that arefree of convection effects will provide new insight into the coupling between thediffusion of chemical species and the thermal transport. Consequently, the objective ofstudying basic reactions in the absence of convection should also contributesignificantly to understanding and accommodating the gravity-induced effects.

2.3.5.10 Concluding Remarks

Supercritical fluids are of both fundamental interest (universality of phase transition,supercritical hydrodynamics) and industrial interest (supercritical solubilisation, oxidation,thermalisation, storage). The field of critical point phenomena has achieved majorbreakthroughs during the past 15 years thanks to microgravity. In particular, a newthermalisation process has been discovered, the ‘piston effect’, which reveals a special typeof hydrodynamics in such near-critical fluids. That study has led to a strong modificationof the prevailing view of critical-point phenomena and even of hydrodynamics. Futureexperimentation on the ISS will certainly lead to further new and unexpected phenomena,which will be of interest for both fundamental and applied science.

Further Reading

Gunton J.D., San Miguel M. & Sahni P.S. 1983, Phase Transitions and CriticalPhenomena (Eds. C. Domb & J.L. Leibowitz), Academic Press, Vol. 8.

Stanley H.E. 1971, Introduction to Phase Transitions and Critical Phenomena,Clarendon Press, Oxford and New York.

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Figure 2.3.6.1. Interface between twoimmiscible fluids A and B.

The interfacial tension σ (red arrow) acts in aplane tangential to the interface at any point P

of the interface itself

some substances are particularly efficient in doing so. In the case of molten metals,particular elements such as oxygen or sulphur have the same effect. These substancesare called ‘surface active agents’ or ‘surfactants’. For water or organic liquids, soapsare only the first and most widely known example of a long list of natural andsynthetic surfactants. All of these molecules have two ends, which respectively ‘like’and ‘dislike’ to be in contact with water and are therefore called ‘hydrophilic’ and‘hydrophobic’ groups. These ‘amphiphilic’ (from the Greek for both) moleculessegregate at the interface, where they can embed their hydrophilic heads in the waterand their hydrophobic tails in the air.

For the so-called ‘soluble surfactants’, an equilibrium is established between theamount of molecules adsorbed at the interface and the amount in the liquid volume.This equilibrium is reversibly shifted as the solution concentration changes. Thesephenomena can be experimentally verified by measuring the surface tension of asurfactant solution as a function of the concentration. As shown in Figure 2.3.6.2,beyond a certain concentration the surface tension becomes practically constant.

This reflects an important property ofsurfactants in solutions. When a criticalconcentration is reached, the excesssurfactant molecules form intoaggregates, called ‘micelles’. These donot contribute to surface activity. Inthese conditions, the concentration offree surfactant molecules is constantand, consequently, the number ofadsorbed molecules and the surfacetension do not change.

2.3.6.2 Adsorption Dynamics

The adsorption process is notinstantaneous, since the transfer of thesurfactant molecules from the bulk tothe interface requires a finite time torestore the equilibrium situation. During this process of adsorption kinetics the surfacetension varies with time, according to the instantaneous value of the adsorption. A surfactant system can be displaced out of adsorption equilibrium, for example by diluting or compressing the adsorbed layer, thereby varying the interfacial area (Fig. 2.3.6.3). Adsorption kinetics also take place on freshly formed interfaces. At thetime of formation, the interface is ideally free from surfactant. A fresh interface caneffectively be created by imposing a large and rapid expansion on an existinginterface.


the capillary pressure P and the interfacial or surface tension σ is thus known as theLaplace equation:

Capillary Pressure P = σ (surface or interfacial tension) x K (surface curvature)

where K is the curvature of the surface (the inverse of its mean radius of curvature).

For common liquids and macroscopic interfaces, the capillary pressure is generallyone thousand times smaller than the atmospheric pressure. Nevertheless, it hasimportant effects on the properties of liquids. For example, the shape of pendant dropsin the presence of gravity is set by the balance of the capillary pressure and thehydrostatic pressure, the latter being due to the weight of the liquid. At a given height,the curvature of the interface, i.e. the drop (or the meniscus) shape, adjusts itself in orderto make capillary pressure consistent with the hydrostatic pressure. Indeed, one of themost used methods for measuring surface tension is based on the analysis of drop shape.

In the absence of gravity, the hydrostatic pressure is zero and so the capillary pressureis constant at each point of the interface, which means that the interface curvature isthe same at each point of the interface. The only closed surface of this kind is thesphere, and this is the shape of free drops in microgravity conditions. Liquid surfacesattached to supports or containers have more complex shapes imposed by thecontact-angle boundary conditions and the requirement of minimum surface area.

Equilibrium values of surface tension can be established for pure systems in times thatare of the order of the relaxation times of atoms or molecules. When dealing with low-viscosity liquids, they are well within the experimentation times. However, whenevermulti-component systems are dealt with, the adsorption processes at the interface,which follow their own kinetic laws, have to be taken into account.

Pure substances are important from a theoretical point of view, because themeasurement of their surface tension can give valuable insight into their atomicconstitution, inter-atomic potentials, bond strength and so on. However, it may bemuch more rewarding from a technological point of view to study multi-componentsystems and to find out the behaviour of the surfaces under ‘normal’ conditions, i.e. inpolluting atmospheres, in the presence of trace elements (impurities or deliberatedopants), or in the presence of chemical reactions.

For pure liquids, the surface tension depends on temperature (and pressure),decreasing when it increases, eventually reaching zero at the critical point. For liquidsolutions, the magnitude of surface tension depends strongly on the composition ofthe interface and decreases as the solutes accumulate at the interface. Almost all polarmolecules are able to adsorb at the surface and reduce the surface tension of water (orof other polar solvents). However, it has been well known since the last century that

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Figure 2.3.6.2. The surface tension of water as a function of CnDMPO concentration (n =10,12,13); DMPO = Dimethyl Phosphine Oxide(after Ravera F. et al. 1997, Langmuir 13, 4817)

interface. Inter-atomic and molecular forces, which are at the origin of interfacialtension, are much stronger than the forces due to gravity. For this reason, interfacialtension is not expected to change in a measurable way when going from terrestrialconditions to a microgravity environment.

Nevertheless, as explained earlier, bulk effects (such as convection) related to gravitycan often obscure phenomena dictated by interfacial tension. The relative strength ofbulk and surface forces can be assessed by using the Bond Number, Bo = ρgL2/σ.Here ρ is the density, g the acceleration due to gravity, L is some characteristic lengthof the system (such as the diameter of a drop) and σ the interfacial tension. On theground, at large Bond numbers, the contribution of the potential gravitational energycompletely overshadows the capillary contribution. Only at small Bond numbers, i.e.when the system dimensions are very small, does the interfacial tension significantlyaffect the shape of the liquid volume.

In the microgravity conditions of a space platform, the Bond number is always nearlyzero (ρg≈0), and so all liquid volumes have outer surfaces whose shape is determinedby their surface-tension value and by the geometrical boundary conditions.Accordingly, space can be used as an environment in which more sensitive and moreprecise surface-tension measurements can be made.

2.3.6.4 Foams

The cellular structure of a liquid foam ismade up of gas bubbles surrounded byliquid, which is in the form of a thin filmwherever two bubbles press tightlytogether. It is familiar in everyday life asa feature of cleaning agents andbeverages. It is a considerable nuisancein many industrial processes thatinvolve liquid/gas mixtures.

In order to control or optimise thebehaviour of foams, it is necessary tobetter understand the properties of thisunique form of matter. Physicists,chemists and engineers can combinetheir expertise here, because effects onvarious scales (those of the thin film, the bubble, and the bulk foam) areinterlinked. The intricate disorderedstructure of a typical foam obeys strict


Two transport mechanisms underlie the progress of the adsorption kinetics. Firstly,there is the interface exchange of molecules with the liquid layer just adjacent theinterface: this is the so-called ‘adsorption proper’. Due to the latter, the concentrationin the layer adjacent to the interface is changed, so that diffusion of the molecules inthe bulk takes place to restore the concentration equilibrium. These mechanisms actat the same time, but develop on independent time scales. Depending on the system,adsorption kinetics can develop on time scales that range from milliseconds, as in thecase of short chain alcohols, to days, as is the case of proteins or long polymers.

2.3.6.3 Interfacial Phenomena and Low-gravity Conditions

Microgravity conditions present a unique experimental environment for the study ofinterfacial and transport phenomena in fluid systems. There is a drastic reduction inthe gradient of the hydrostatic pressure. Consequently, the effects driven by capillaryforces, differences in chemical potentials and other mechanisms are enhanced orisolated. In particular, in order to adequately study adsorption kinetics at fluidinterfaces a simple geometry for the surface is required, together with the absence ofgravity-driven convection, which could deform the bulk diffusion profile near the

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Figure 2.3.6.3. Schematic of adsorbed molecules at a free surface. If the surface isstretched or compressed, molecules are displaced from or to the surface, so that thesurface tension changes in a dynamic manner

Figure 2.3.6.4. A foam is often formed bybubbles rising in a liquid (photograph courtesyof J. Cilliers, UMIST, UK)

In recent years, this eventful life history has been chronicled in some detail. It hascome to be well understood only in the limit of a static, dry foam. In part this limitationis due to experimental obstacles because a wet foam rapidly drains in normal gravity.Attempts to circumvent this difficulty include the trick of continuous addition of freshliquid (forced drainage). In that case, a hydrodynamic instability intervenes to limit theeffectiveness of the procedure. Another solution is to use very small bubbles, as theabove equation would suggest. This is not easy, and speeds up the coarsening process.Uniform wet foams in equilibrium can, however, be made by taking advantage of themicrogravity environment of space. By careful measurement of their properties inmicrogravity, it is expected to be possible to extend the range of present theories. Thisapproach also adds a new dimension to foam technology.

2.3.6.5 Emulsions

Immiscible liquids are often found inindustrial processes. If they are mixedtogether and shaken, a dispersion ofsmall droplets of one liquid into the otherphase is obtained, i.e. an emulsion hasbeen formed (Fig. 2.3.6.6). Emulsionsoccur in natural products (oil, milk), infoods (mayonnaise), pharmaceuticals,cosmetics, and many other agriculturaland industrial products.

In some cases, such as that of foods,emulsions have to be stable, i.e. theyhave to retain their original properties. Inother cases, they have to be destabilisedin order to recover the individualconstituents, for example in oil recovery.The control of stability is therefore one of the most important problems in emulsionscience and technology. Efficient, safe and cheap ways of stabilising (or destabilising)a crude-oil emulsion can make all the difference to the economy of an oil field. Hence,the oil industry actively supports such projects related to crude-oil recovery. The crudeoils are emulsions either of water in oil or of oil in water, stabilised by naturalsurfactants (asphaltenes). Stabilisation/destabilisation is relevant to all productionsteps, from drilling to refining, as regards both emulsions and foams.

There are many factors and mechanisms at work in emulsion destabilisation. Amongthem are: ‘aggregation’, in which different droplets of the dispersed phase aggregatein clusters, ‘coalescence’, in which two or more droplets fuse together, and ‘Ostwaldripening’, in which the liquid contained in a smaller drop diffuses to a neighbouring


rules of equilibrium, which dictate its local geometry. These rules were demonstratedby the Belgian scientist Joseph Plateau in the 19th century.

The foam can never be regarded as entirely static, unless it has been solidified. That isthe situation in the common polyurethane foams, or in the more unusual metallicones, which are described below. As long as it has a liquid component, the foamevolves under the action of three processes: drainage, coarsening and rupture.

‘Drainage’ is the term applied to the motion of liquid through the foam. Usually, afreshly made foam is left to stand and gravity extracts most of the liquid from it.Eventually, an equilibrium profile of density (or liquid fraction) as a function of heightis established. The remaining liquid is held up by surface tension. Only very close tothe underlying liquid is the foam ‘wet’, i.e. with a liquid fraction of more than about15%. There is a useful approximate rule-of-thumb whenever the foam is in contactwith underlying liquid. In equilibrium:

Thickness of wet foam layer = l02 /d

where d is the average bubble diameter, and

l02 = σ / ρg

For example, both l0 and d might be of the order of 1 mm, in which case only the wetfoam consists of only a single layer of bubbles, in normal gravity.

‘Coarsening’ is the increase with time in the average size of bubbles. This is due to thediffusion of gas through the thin films, due to pressure differences. Generally speaking,this proceeds from small to large bubbles and so continually eliminates the smallerones. In the final stage of the life history of a foam, the ‘rupture’ of thin films eventuallytakes over and causes it to collapse.

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Figure 2.3.6.5. Effects on various scales are interlinked in foams

Figure 2.3.6.6. Schematic representation ofstabilisation/destabilisation and phase-inversion mechanisms in emulsions

particles on the strength of gravity was found, but there was no detailed analysis.Nevertheless, this was a useful pointer to the practical use of this technique in space,for waste treatment or for biological sample processing. Similarly, a number ofinteresting experiments were carried out on foam drainage, but the interpretation wasrudimentary.

More recently, the Meudon group of M. Vignes-Adler has used parabolic flights to varygravity while creating and observing aqueous foams. The detailed structure ofsamples of about 100 bubbles was captured and analysed by optical tomography, sothat it was even possible to identify the precise shape of every bubble.

Another European group, at the Fraunhofer Institute in Bremen (D), has embarked onthe fabrication of metallic foams in microgravity. Nowadays many substances can beformed as solid foams, among the more surprising being glasses and metals.Fabrication methods have steadily progressed to the point at which a wide variety ofalloys may be processed, and there is some limited control over their structure.Further development is motivated by emerging markets for this product, particularlyfor structural and energy-absorbing automobile components.


larger one due to the different surface curvatures (Fig. 2.3.6.7). In all cases, the twophases are subject to gravitational forces and tend to eventually ‘cream’ to the surface,or ‘settle’ to the bottom, as a function of their relative densities. Creaming, Ostwaldripening and coalescence are closely analogous to drainage, coarsening and rupture,in the terminology of foam physics.

Advances in the control of emulsion stability can be achieved by increasing ourknowledge of the elementary mechanisms already mentioned, and the processes ofadsorption and transfer of surfactants that underlie them.

2.3.6.6 Microgravity Projects

- Foams

There have been occasional microgravity experiments on foams over recent decades,conducted by American, Canadian and European teams. For the most part, they havebeen quite preliminary and exploratory. They suffered from the poorly developed stateof the theory at the time, which made it difficult to frame precise questions forexperiments to address.

In the early nineties, for example, foam flotation in a microgravity environment wasinvestigated using parabolic flights sponsored by NASA. Foam flotation is animportant industrial process, in which suspended matter is removed from a liquid byadsorption in a foam. As expected, a strong dependence of the size of recovered

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Figure 2.3.6.7. Destabilisation mechanisms in emulsions: segregation occurs in agravitational environment, due to the different specific weights of the two phases

Figure 2.3.6.8. Experimental system used for the observation of foams in microgravity(from C. Monnereau et al. 1999, J .Chim. Phys., 96, 958)

The creation of a solid metal foam is a race against time. Once formed in the liquidstate, it must be frozen quickly enough to avoid drainage and collapse. Again gravityis the enemy. Fabrication in space raises fascinating possibilities: it should be possibleto greatly extend the range of alloys, eliminate additives that have served to increaseviscosity, and produce superior-grade materials.

Two international projectswere recommended forESA funding in 2000,under arrangements thatallow for terrestrialresearch in the first instance, and are aimed at the eventual utilisation of theInternational Space Station. ‘Hydrodynamics of Wet Foams’ is coordinated by GuyVerbist, of the Shell Research Laboratory in Amsterdam. His team plans to studydrainage, particularly of wet aqueous foams. ‘Development of Advanced Foams underMicrogravity’, co-ordinated by John Banhart of the Fraunhofer Institute, is primarilydevoted to metallic foams. Both projects are concerned with the development of newmethods of monitoring foams in real time, so as to enhance the quality of the dataavailable for comparison with theory.

- Emulsions

The ESA ‘FAST’ and the subsequent ‘FASES’ projects aim to establish a quantitative linkbetween emulsion stability and the physical chemistry of droplet interfaces. Researchgroups from Italy, Germany and France are co-operating at three levels ofinvestigation. These are:

(a) the study of adsorption dynamics with transfer of matter and interfacial rheologyof liquid/liquid interfaces

(b) the study of drop–drop interactions and of the physical chemistry of the interfacialfilm

(c) the study of the dynamics of phase inversion in model emulsions.

The projects, supported also by the ESA Topical Team ‘Progress in Emulsion Scienceand Technology’, co-ordinated by R. Miller of the Max-Planck Institut, Berlin, include


Figure 2.3.6.9. Equipment for metallicfoam formation used on parabolicflights (courtesy of the FraunhoferInstitute, Bremen, Germany)

Figure 2.3.6.10. A typical metallic foamencased in a cylinder. This new materialoffers many advantages in terms ofweight, strength and energy-absorbingcharacteristics (courtesy of J. Banhart)

Figure 2.3.6.11. Foam sample in twodifferent gravity environments (courtesy ofMonnereau et al.)

b

a

Figure 2.3.6.12. Schematic of the Capillary PressureTensiometer. A drop of fluid 1 is formed inside anotherimmiscible fluid 2 by the action of a piezo-electricactuator, and the capillary pressure is measured as afunction of the drop diameter. The surface tension canbe calculated by means of Laplace’s law

In addition, emulsions play an extremely important role in metallurgy, when dealingwith metallic systems that show miscibility gaps in the liquid state. Experiments with metallic Al-In emulsions have shown that other mechanisms can exist that maydestabilise the emulsion, in particular Marangoni motions and wall effects. Theseeffects were confirmed on metallic Cu-Pb emulsions in 1993. Sounding-rocketexperiments had also been conducted in 1982 to test acoustic mixing devices toprepare Pb-Zn emulsions directly in microgravity conditions. It is worth noting that theMarangoni studies in microgravity conditions have led to important improvements inindustrial metallurgical processes, particularly in the case of metallic emulsions forbearing alloys. Marangoni effects, with specific parameters evaluated in microgravity,can be used to counteract the gravitational pull on the ground. This procedure allowshomogeneous dispersions of the softer (lubricating) phase to be obtained duringcontinuous casting processes.

Acknowledgements

This contribution has benefited from discussions with members of the ESA TopicalTeams:– ‘Foams and Capillary Flows’, co-ordinated by D. Weaire. Members: J. Banhart,

V. Bergeron, B. Kronberg, D. Langevin, P. Georis, G. Verbist, M. Vignes-Adler,D. Wantke, K. Lunkenheimer and J-C. Legros.

– ‘Equilibrium and Dynamic Properties of Adsorbed Layers’, co-ordinated byA. Passerone. Members: L. Liggieri, R. Miller, G. Pétré, G. Loglio, A. Steinchen andA. Sanfeld.

Further Reading

Ivanov I.B. 1988, Thin liquid films, fundamental and applications, Surfactant Sci., Ser.No. 29, M. Dekker, New York.

Ivanov I.B. & Kralchevsky P.A. 1997, Stability of emulsions under equilibrium anddynamic conditions, Colloid and Surfaces A, 128, p. 155.

Moebius D. & Miller R. 1998, Drops and Bubbles in Interfacial Research, Elsevier,Amsterdam.

Passerone A., Liggieri L. & Ravera F. 2001, in Physics of Fluids in Microgravity (Ed. R.Monti), Gordon and Breach, ESI Book Series, Vol. 8.

Schramm L.L. (Ed.) 1992, Emulsions: Fundamentals and applications in the petroleumindustry, Adv. in Chem. Ser. 231, Am. Chem. Soc.

Weaire D. & Hutzler S. 1999, The Physics of Foams, Oxford University Press.


experiments in the laboratory, onsounding rockets (Texus, 1993), and onShuttle-Spacehab missions (1998,2001) (Figs. 2.3.6.13 and 14).Continuing work on the InternationalSpace Station is envisaged.

Drop deformations have also beenstudied in drop-tower experiments,whilst programmes aimed atdeveloping new theoretical models

and space experiments are being conducted in the United States and financed byNASA. The rheology of interfaces and of concentrated emulsions, the mobility ofbubbles and drops, as well as thermocapillary/Marangoni effects, drop formation/break-up and phase separation, are increasingly attracting the attention of researchers.

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Figure 2.3.6.13. The layout of the CapillaryPressure Tensiometer, constituting the core ofthe FAST facility

Figure 2.3.6.14. The FAST facility, flown onShuttle mission STS-95 in October 1998

Figure 2.3.7.2 reveals that almost threequarters of the greenhouse emissioneffectively originates from industrialcombustion, power generation andtraffic. Since the CO2 emissions fromcombustion (Fig. 2.3.7.3) can really onlybe lowered through the use of moreefficient systems, a reduction in the useof fossil fuels is generally required.

2.3.7.2 Activities and Results in theDifferent Branches of CombustionStudies

In accordance with the three main typesof combustion, the activities and resultsreported here are divided into three sub-areas: premixed, diffusion-flame andcondensed-matter combustion. Each ofthese represents different, typicalterrestrial energy-conversion processes.Whilst premixed and diffusivecombustion deal with gaseous fuels,condensed matter first needs to bevaporised before combustion is possible.In some cases, there is technical overlapbetween these branches. The recentintroduction of a fourth sub-area, that ofnon-intrusive diagnostics, acknowledgesthe major developments in this area thathave been triggered by the specificdemands of microgravity researchfacilities. These have led to inventionsthat have proved of great terrestrialbenefit research, both in laboratories aswell as in industrial applications. Thesediagnostics are increasingly finding theirway into the closed-loop control systemsthat serve to optimise combustionprocesses.


2.3.7 Combustion

C. Eigenbrod


Combustion is the process of transforming chemical energy into thermal energy. It isstill the most important process for delivering energy to industrial processes, forelectrical power generation, for the propulsion of cars, ships and aircraft, and last butnot least, for the heating of homes, which ensures the existence of mankind outsidethe tropical and subtropical regions.

In most cases, combustion leads to a temperature rise and is accompanied by adecrease in the local density, generally by a factor of two to ten. This density changegives rise to buoyancy effects in many terrestrial combustion processes. Byeliminating buoyancy and thus reducing the number of degrees of freedom,microgravity experiments can be of great benefit for the observation andunderstanding of basic combustion phenomena.

Numerical calculations, taking advantage of the increasing capacities of moderncomputers, have become the most important tool for developing new or bettercombustion technologies. However, the quality of the results from such calculationsdepends upon the quality of the basic input data, as well as the accuracy of the model.Consequently, the data derived from microgravity experiments can assist in thedevelopment of simulations by offering an improved material-properties database, in particular by providing validational help at a stage in development where naturalconvection-driven buoyancy has not yet been included.

Energy generation through the combustion of fossil fuels can and will be replaced byother energy sources to a substantial degree in the future, for example for electricalpower generation. Nonetheless, mankind will need to rely upon such fuels forpropulsion purposes for the foreseeable future. The combustion of these fossil fuels isinherently connected to both the consumption of finite resources, and the productionof pollutants. Some major exhaust byproducts are themselves poisonous, such as CO,N2O and soot. For others, like CO2, SOx and NOx, the interaction with the global climateis more complex. Even though the energy consumption per capita will dropsignificantly in industrialised countries in the future, overall world consumption willactually rise, as the EC prognosis depicted in Figure 2.3.7.1 shows. This is due to thecombined effect of the increase in population and the rise in per-capita energyconsumption in the newly industrialising countries.

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Figure 2.3.7.1. European Commission (EC)prognosis for future worldwide energyconsumption

Figure 2.3.7.2. The origins of, and percentagecontributions to, the greenhouse effect(courtesy of the World Resources Institute)

Figure 2.3.7.3. The percentages of trace gasesdriving the greenhouse effect (courtesy of WorldResources Institute)

homogeneous mixture even with short mixing lengths. Turbulence also leads to longer,wrinkled flame fronts. This would then result in the desired side effect of more flamesper unit volume and thus smaller combustion chambers. As can easily be imagined, alean flame, propagating slowly and just barely ‘alive’, is rather sensitive to bothfluctuations in mixture ratio as well as to turbulence. Put simply, blowing into a flamewill augment the combustion, at least until the local velocity becomes so high as toseparate the flame from the unburnt fuel. Extinction, at least locally and temporarily,is then the outcome.

Another gas-turbine-specific problem is related to periodic combustion phenomenathat are assumed to be based upon design criteria, such as the number of revolutionsper minute, the number of individual burners, the periodicity within the swirl-stabilised burners, and also the contours of the combustion chamber, serving as aresonant body. Because of that, these engines tend to fall into a noise-generating,oscillating operation mode, with associated pressure waves that can limit the lifetimeof the engine and possibly even destroy it.

This touches on the second microgravity aspect, as it is not yet well understood howa lean, more or less premixed flame interacts with high levels of turbulence. Highturbulence intensity in this case means small, highly energetic vortices. These vorticesare so small that they are not only assumed to transport reacting layers through agiven volume, but can also interact directly with a flame front with a typical thicknessof the order of a tenth of a millimetre. If this interaction leads to local flame extinction,there will be fluctuations in local heat release. That in turn might lead to pressurefluctuations and, inside a resonant body, to the well-known ‘humming’ phenomenon.It is an open but important question whether such flame-vortex interaction is thesource, or at least the amplifier, of combustion-induced oscillations. The interaction ofa premixed flame with rather large turbulence eddies is well understood, but the effectof small eddies, having the dimensions of the flame-front thickness, is unknown.


- Premixed Combustion

In premixed combustion, the reactants are well mixed prior to initiation of thecombustion process. The majority of technical processes in gaseous combustion fallinto this category. The temperature of premixed flames can be adjusted by changingthe fuel-to-oxidant ratio. Usually, premixed flames are of low luminosity and aretherefore more suitable for turbines than for heat exchangers. In a turbine, advantageis taken of the thermal expansion of the gas, while a heat exchanger requires radiativeheat transfer from the luminous flame to the separating walls in order to be efficient.An important example of this is the gas turbine, used in natural-gas-fired powerstations. The biggest single gas turbines currently in use have an electrical poweroutput of about 300 MW. When operated in a combined cycle with steam turbinesthat use the steam generated from the gas turbine’s exhaust heat, such powerstations achieve efficiencies of about 60%. Centralised power generation will continueto be needed for the foreseeable future and, with the demand for higher profitability,even bigger assemblies will be required to optimise the installation costs per MWh.

The formation of nitric oxides (NOx), which are both poisonous and environmentallyharmful, is mainly determined by the combustion temperature. Therefore, thistemperature should never exceed 1500˚C, which is the onset temperature for theformation of thermal NOx through the Zeldovich-mechanism. Operation below thisrather low combustion temperature requires very lean mixture ratios (i.e. much air –little fuel), close to the flammability limits of natural gas.

This then leads to the first issue, which is addressed by research in microgravity. Whentrying to determine experimentally the flammability limits of a fuel gas/air premixtureon the ground, the results are different for upward- and downward-propagating flamesdue to buoyancy effects. In microgravity, where buoyancy does not affect the diffusiveprocess, it was possible to determine the true minimum air/fuel ratios. These valuesare below those found under terrestrial conditions (Figs. 2.3.7.4 and 5). These resultssupported the validation of chemical kinetics equations that were to be implementedin terrestrial combustion simulation. Microgravity experiments also revealed thetendency for propagating lean methane/air flame fronts to wrinkle and maybe laterto form independent cellular flames. These phenomena were first observed by P.Ronney in hydrogen/air flames in microgravity.

Operation of a gas turbine at air/fuel ratios close the flammability limits is onlypossible if the mixture is perfectly premixed, but in reality this is hard to achieve. Itwould require a long duct to allow complete turbulent mixing of the separatelyinjected reactants. As the air coming from the compressor is as hot as 400 to 600˚C,self-ignition of the mixture could occur prior to its arrival at the combustion chamber.Thus the mixture has either to be richer, in order to avoid it being locally below theflammability limits, or the turbulence must be high enough to guarantee a

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Figure 2.3.7.4. Flammability limits formethane/air under 1g (top) and µg(courtesy of Hyvönen & Peters)

Figure 2.3.7.5. Flame propagation for 60bar and 5.01 vol% methane (front recordedat 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9, 1.1,1.3, 1.5 sec). 50 mm diameter Schlierenimage (courtesy of Hyvönen & Peters)

combustion are the controlling factors. Despite their importance, there remains a lackof fundamental knowledge of these processes.

Microgravity provides an ideal environment in which to study these basic diffusion-controlled processes of combustion and particulate formation, without the maskingeffects of natural convection. The well-developed flamelet concept, used for modellingreal turbulent combustion processes, is based upon superposition of the diffusion-controlled basic reactions with a turbulent transport. Thus, the accuracy of numericalcalculations applying this widely used method depends upon the accuracy of thefundamental data. Microgravity experimentation and modelling is therefore theappropriate way to move from semi-empirical methods to a knowledge-based simulation.

Compared to 1g flames, the microgravity gas-jet diffusion flames have much greatertendencies to emit soot or other particulates. This is due to longer residence times andthus greater time for particulate formation, plus broader regions in which compositionand temperature are favourable for particle formation. Recent quantitative measure-ments show peak soot-volume fractions about twice as high in microgravity as in 1g,for 50% acetylene/50% nitrogen-air flames. In addition, in microgravity the particlescan agglomerate to form much bigger aggregates. This is because with weakconvection, thermophoretic forces, which move particles towards lower temperatures,are an important effect. If the convectionand temperature gradients are in thesame direction, the convective andthermophoretic forces may balance atsome location. This leads to sootaccumulation inside the flame front inmicrogravity.

In order to study the formationmechanisms of soot and otherparticulates, microgravity experimentshave been proposed within another ESAMAP project, applying a laser-basedmethod to measure, in-situ, the sizes andgrowth rates within flames. Figure2.3.7.6 shows the local size distributionof primary soot particles formed in alaminar ethane/air jet-diffusion flameunder 1g conditions. Applying thisquantitative method in microgravityconditions promises to yield muchdeeper insight into the formationprocess.


The most basic experimental configuration needed to investigate this phenomenon isa lean, premixed propagating flame, running into an artificially produced vortex withwell-defined properties. As the freely propagating flame on Earth is affected bybuoyancy, as explained above, microgravity is needed to establish the requiredexperimental conditions. Research teams in the USA and in Europe are preparing suchmicrogravity experiments, with participation by industry. An ESA-supported TopicalTeam of experts has formulated the appropriate questions and the experimentalhardware is being prepared within the framework of a Microgravity ApplicationPromotion (MAP) project.

Modelling and simulation of turbulent combustion is a rather well-developed andintegral part of commercial Computational Fluid Dynamics (CFD) tools. The inclusionof information on small eddy interactions can become an important enhancement,leading to better predictability of the behaviour of future highly efficient engines.

- Diffusion Flames

In diffusion flames, the fuel and oxidiser are unmixed prior to the initiation ofcombustion. Consequently, they must diffuse towards each other in order to react. Theflame is always established close to the stoichiometric region within theconcentration-gradient field. Stoichiometry is the equivalence ratio where the oxidiserconcentration is exactly that which is necessary to completely burn the fuel.Stoichiometric flames are the hottest possible for the given fuel and the temperatureis always beyond 2000˚C.

Therefore, a priori control of the NOx emissions is not possible. On the contrary, assuch flames are used technically for, for example, process heat generation, a certainamount of particulates is often needed. These particulates are radiation emitters. Theymake a flame luminous and therefore serve to provide for efficient heat exchange fromthe flame to the walls of, for example, a steam generator, or to the material to beheated when producing melts of glass, ceramics or steel. In order to control pollutingemissions, engineers are thrown back to an appropriate but costly post-treatment ofthe exhausts. To optimise such a system in terms of the highest efficiency coupledwith the lowest or least harmful amounts of exhaust pollutants, detailed knowledge ofthe kinetics of diffusive combustion is required.

Another technical application of diffusion flames that is of increasing importanceconcerns the flame products. Carbon particulates, for example, are used for printingtoner or serve as filler for tyre production, not only to colour them, but also forperformance adjustment. Diamond thin films and coatings for hardening tool surfacescan be combustion generated and deposited on metal surfaces. The same is true forother carbides, for example those based on silicon that can be flame-generated anddeposited. In all of these cases, the physico-chemical processes of diffusive

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Figure 2.3.7.6. Size distribution andlocation of primary soot particles formedin the upper section of a laminar ethane-air jet-diffusion flame at 1g (courtesy ofProf. S. Will)

diagnostics needed to answer the related questions, microgravity research would bedispensable. But since terrestrial diagnostics can only be applied to the spray in total,and since even the most sophisticated non-intrusive laser diagnostics fail whenapplied to a dense spray, microgravity is the most promising way out. This researchhas already found that under engine operating conditions, droplets can ignite in astaged regime with exothermal precursor reactions affecting the total induction timeuntil hot ignition. Figure 2.3.7.7 shows the refraction-index distribution, which islinked to the temperature distribution, observed around an igniting droplet at differentstages. These results led to the definition of new model kerosene and light-oil fuels,including staged-ignition behaviour. The model fuel data are needed to enablenumerical simulations to transfer those findings into process simulations.

In addition, the droplet spacing obviously plays a role. Droplets in a spray do notnecessarily ignite individually, but when auto-ignition occurs at a preferred point theassociated heat release might induce ignition of the whole volume. Figure 2.3.7.8shows results from microgravity experiments, where development of the cool flame isindicated by the very weak chemo-luminescence of formaldehyde, which is a stableproduct of the cool-flame burning prior to hot ignition. For the given conditions, the 5 mm distance causes ignition to happen first, while the single droplet does notundergo hot ignition. This is assumed to result from a balance between the dropletssheltering each other (delaying ignition) and the fuel-vapour concentration rising morein the space between the droplets (impelling ignition). Numerical studies are requiredto find out which kinetic aspects are really responsible for this complex nonlinearbehaviour.

As the translation of data from microgravity experiments into technical applicationswill be achieved through numerical simulation, knowledge of the detailed physical andchemical process is much more important than the question of whether or notexperimental and technical conditions are directly comparable. In this respect, theability to produce large droplets, which are very different from those in realapplications in terms of size and thus induction times, is not a drawback, but a perfectcondition for studying the whole process.


- Condensed-Matter Combustion

The term ‘condensed matter’ refers in this context to fuels that are initially liquid orsolid. As the combustion process itself can only happen in the gas phase, heating andvaporisation or gasification processes must be introduced. Whether the subsequentcombustion is of the premixed or diffusion type depends upon the uniformity of thefuel-gas/oxidiser mixture that can be established, prior to initiation of the combustionprocess. The majority of technical combustion systems fall into this category,including internal combustion engines (petrol and diesel), aircraft turbines, rocketpropulsion, heating-oil burners, coal-fired power stations, etc.

Another important aspect that falls within this sub-area is fire safety. Dust explosionsand smouldering combustion, with subsequent flash-over, are just two examples. Theinteraction with flames of the water sprays used for fire fighting, aiming at flamequenching through heat deprivation, is a kind of inverse combustion, but it followsidentical rules.

An aircraft-type kerosene-fuelled gas turbine is pretty much comparable to the gas-fired power generators type discussed above. Several European Commission (BriteEuram, Low NOx III) and various national research programmes are directed towardsachieving a reduction in NOx emissions from aeroengines.

Whenever a fuel spray is injected into a flame, the combustion will be of the diffusivetype, because the droplets cannot vaporise straight away. After heating up and duringvaporisation, the droplets’ surface temperature remains close to boiling temperature.The already gasified fuel burns at the stoichiometric concentration area in the vicinityof the droplets. The result is high local temperatures and thus high NOx emissionvalues, even though the overall mixture ratio was in the lean regime. The aim istherefore to ensure that the local mixture ratios are the same as that of the overallmixture, which is only possible with premixtures. One intended technical approach isthe LPP (Lean Pre-vaporised Premixed) combustor, with each burner equipped with anadditional premixing duct where vaporisation and turbulent mixing occurs before themixture enters the combustion chamber. As state-of-the-art compressors deliver inlettemperatures of 600˚C or more, and the trend in development is to exceed 800˚C, the time for vaporisation and mixing is very limited before self-ignition occurs.In the case of a lightweight and thus comparatively fragile aeroengine, a resultingflashback, or even worse, a stabilised flame inside the premixing zone, isunacceptable. Detailed knowledge of the auto-ignition behaviour of a spray istherefore a prerequisite for effective design. Knowledge is definitely lacking in this area.

If a droplet could be followed from the injection nozzle, through the premixing areaand into the combustion chamber until burnout, accompanied by the non-invasive

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Figure 2.3.7.7. False-colour interferograms of a self-igniting, suspended n-heptane dropletin microgravity. From left to right: cool vapour area around the droplet, bright-green coolflame above ambient temperature, cool flame expanding, and hot ignition

The transformation from microgravityexperiments on single particles totechnical combustion will follow thesame numerical pathway as fromdroplets to sprays.

Another example of condensed-mattercombustion is fire. It is the worst thingthat can happen onboard a spacecraft, because there is no easy way to escape from itand its poisonous combustion products. Fire prevention is therefore an extremelyimportant issue in space.

On Earth, the energy released by a fire strongly depends upon buoyancy. Inmicrogravity, buoyancy is absent and the only convection process driving a fire is thatinduced by the air-conditioning system. Thus, fires in space are usually much lessvehement than on the ground. However, what looks like an advantage at first sight isparticularly dangerous when looked at more carefully. Experience shows that fires inspace can remain undetected until they have propagated and spread over wide areas.Besides the direct hazard, the fire can inflict a lot of damage, maybe even affecting thelife-support systems.

All materials used in space vehicles need to meet specific flammability requirementsthat, in NASA’s case, are provided in the document ‘Flammability, Odor, Offgassingand Compatibility Requirements and Test Procedures for Materials in Environmentsthat Support Combustion’ (NASA-NHB 8060.1) This document specifies two tests thatneed to be performed before a material is qualified for use in a space vehicle: theupward flame-propagation test (Test 1) and the heat- and visible smoke release rates test (Test 2). These two tests are expected to properly assess the flammability ofmaterial in microgravity conditions. Experimental and numerical research conductedon the basic items have questioned the reliability of the results obtained with thatprotocol. In fact, behaviour has been found that is the reverse of that originallypredicted. However, it is clear that the methods currently applied are not based on atrue understanding of the phenomena, but rather on a semi-empirical strategy.


In another recently started ESA MAP project, partners from universities and theEuropean gas-turbine industry will together investigate these issues. This projectenhances the value of both the microgravity and ground-based experiments. Theseexperiments will serve to validate the ‘numerical pathway’ from the space research tothe practical engine application.

Coal combustion still plays the predominantrole in electrical energy generation.Optimisation of the combustion process is allthe more important because coal isinherently linked with comparatively highpolluting exhaust contents. Unlike fueldroplets, the coal dust particles used inboilers for steam turbines are not sphericaland are heterogeneous in consistency.Ignition of a particle exposed to the hotenvironment in a combustion chamberhappens first at the surface of the coke pores.A noticeable temperature rise is firstobserved in the gas phase, followingpyrolysis of the volatiles released by theparticles. The remaining coke burns longestand contains the majority of the primaryenergy. In contrast to droplets, coal particlesstrongly absorb infrared radiation. Thus,particle heating is controlled by radiationinstead of by heat conduction, as occurswith droplets. Radiation is absorbed at thesurface, and so it is easy to imagine that thecorners heat up quicker than the flat regions.As a sphere exposes the smallest surface perunit volume, the heating process is expectedto be shorter the more the particle’s shapediffers from a sphere. For a given origin-dependent coal property, the efficiency ofcombustion as well as the composition of theprimary exhausts is determined by theinitialisation process – the ignition of both the volatiles and the coke.

In order to develop particular numerical coal-combustion models, detailed informationabout the initial phase of combustion is required. The first experiments on specificallyshaped particles of Assam brown coal in microgravity revealed the expecteddependency of induction times on specific surface (Fig. 2.3.7.9).

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Figure 2.3.7.8. Chemi-luminescence offormaldehyde forming around self-igniting n-decane droplets at 1 barand 430˚C. Droplet initial diameter1.5 mm. From left to right: a singledroplet (no ignition); 3.5 mm centredistance; 5 mm centre distance; and6.5 mm centre distance. The pictureswere taken with an intensified high-speed CCD imager

Figure 2.3.7.9. Comparison of inductiontimes until release of volatiles (tvr) anduntil volatile ignition (tvi) for different basicparticle shapes. Each data columnrepresents 10 experiments, performed atthe HNIRI 10 m drop facility in Sapporo.Coal: Assam brown. Heating: ~ 1000 K/s(with spot heaters)

Figure 2.3.7.10 is a schematic of the laserdiagnostic system at the Bremen drop tower.This installation was used for two-dimensionaldiagnostics of species concentrations. Thehydroxyl radical was used as an indicator ofthe reaction area in flame, whilst theformaldehyde molecule, a stable product oflow-temperature reactions, providedinformation on the processes precedingignition. The method applied is Laser-InducedFluorescence (LIF), a scattering technique inwhich only the molecules of interest areexcited to fluorescence by highly energeticlight with an extremely narrow spectral distribution, coinciding with the energydifference between the excited state and the equilibrium state of the specific species.

Both the limited time available in a drop experiment, as well as the transient nature ofthe combustion process itself, led to the development of a diagnostic system withcomparably high repetition rates of up to 250 frames/second. As an example, Figure2.3.7.11 shows selected OH-LIF images of a methane/air jet-diffusion flame duringtransition from the flickering 1g shape to the quasi-steady tulip-shaped microgravityflame. From this experiment, it was learned that microgravity flames are associatedwith surprisingly high rates of radiative heat loss. These can even lead to a flameoutline that is not necessarily closed, but can build an open tip.


Joint project groups of scientists from Europe and the USA have defined anexperimental approach to study systematically the role of the different modes of heattransfer and the influence of flow pattern and oxygen content in the gas phase. Themechanism of ignition, flame spreading and stability, as well as quenching, blow-offand other modes of extinction, will also be studied in a configuration correspondingto Test 1. The results will be incorporated into the existing body of theory. The aim isto define a new protocol to classify the potential fire hazards of specific materialsbased on fundamental understanding, rather than empirical worst-case scenarios. Theresults may therefore affect current regulations regarding material selection formicrogravity environments, and this research also has the potential to improve fireprevention and fire fighting on Earth as well as in space.

- Non-Intrusive Diagnostics

Diagnostic methods, most of them laser-based and more or less non-intrusive, havebeen developed during the last fifteen years. These methods have provided impressiveinsight into the basics of physical chemistry in combustion. The unique properties ofcoherent laser light and its interactions with matter make it possible today to measureflame temperatures, short-lived chemical intermediates, flow patterns, concentrationfields, and even the temperature distribution inside heating droplets. Not least, thiscan be done without probing, and therefore without affecting the process of interest.These developments are mainly the result of work by physical-sciences institutes inEurope and the USA in close co-operation with combustion researchers.

Fundamental combustion research in general, and particularly that performed undermicrogravity conditions, requires diagnostic methods that are able to present datawith an accuracy and resolution appropriate to the exacting conditions. However, thetransformation of these techniques from terrestrial laboratories to microgravityfacilities has been slow. As a result, the methods applied to microgravity combustionwere restricted for a long time simply to photographic or video observation, due partlyto the mass and power limitations inherent in orbital facilities. It was also due to thecomplexity and sensitivity of the optical installations and the potential hazardsassociated with lasers that had to be dealt with. It is not surprising, therefore, that thedrop towers in Bremen (D) and in Cleveland (USA) were the first facilities to adapt thetechniques to microgravity combustion research.

One of the reasons why drop towers are used extensively for combustion research isthat combustion processes generally have short time scales and thus suffer less fromthe limited microgravity time available in such facilities. The other is that the largest,most sensitive and most electric-power-consuming elements of laser diagnostics neednot be dropped together with the experiment. The laser light can be either mirrored(Bremen) or fibre-transmitted (Cleveland) into the falling capsule.

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Figure 2.3.7.10. The laser diagnostic system atthe Bremen drop tower. The 1 ton excimer lasersystem remains attached to the top of the droptube. The pulsed laser is mirrored into the fallingcapsule

Figure 2.3.7.11. Selected OH-LIF images of a methane/air jet-diffusion flame duringtransition from 1g (left two images) to microgravity. Each image in the upper row was taken4 ms before the corresponding image in the lower row (courtesy of L. Sitzki)

pay off. In most cases, the microgravity combustion research issues are far fromimmediate application, which means that a single company cannot be expected tobear all of the research costs. In specific cases, it might be different for a pool ofEuropean companies. In general, however, the outcome of microgravity combustionresearch, at least initially, will be in the form of publications, which need to be carefullysurveyed and fostered.

Perhaps one example may serve to illustrate here the point concerning the benefitsthat adherence to a long-term programme can bring. At present, no turbinemanufacturer in the world, in either the power-generation or propulsion business, couldstay in the market without using monocrystalline turbine blades. However, every suchmanufacturer has to rely on the knowhow of a US-based monopoly. Costly, extensivetrials by European manufacturers to catch up in this knowledge have failed. Eventhough the US initiative had a military background, the critical knowhow was gainedfrom a long-term research programme financed through NASA. Fundamental researchin microgravity played a dominant and vital role within that long-term programme.

Further Reading

Eigenbrod C. 1998, European Microgravity Combustion Science, from Drop Towers tothe Space Station. In: European Interest in the Scientific Utilization of the InternationalSpace Station – Fluid-Physics, Material Sciences and Combustion, European Academyof Sciences and Arts, Vol. 22, No. VIII.

Hyvönen J. & Peters N. 1998, Experimental Determination of Lean Flammability Limitsof Methane-Air Mixtures at High Pressures under Microgravity Conditions, Proc. DropTower Days, October 1998.

Ronney P.D. 1998, Understanding Combustion Processes through MicrogravityResearch. In: Proc. 27th Int. Symp.on Combustion, The Combustion Institute, Boulder,pp. 2485 – 2506.

Sitzki L., Tittmann K., Tischer S., Rau H., Hinrichs O., König J. & Rath H.J. 1998,Experiments and Numerical Simulation of Hydrogene, Methane, Propane and ButaneDiffusion Flames under Microgravity, Proc. 27th Int. Symp. on Combustion, TheCombustion Institute, Boulder.

Will S., Schraml S., Bader K. & Leipertz A. 1998, Performance Characteristics of SootPrimary Particle Sizes Measurments by Time-Resolved Laser-Induced Incandescence,Applied Optics, Vol. 37, pp. 5647 – 5658.

Williams F.A. 1995, Combustion Science. In: European Low-Gravity Physical Sciences inRetrospect and in Prospect, ELGRA Assessment and Peer Evaluation.


This diagnostic system, which resulted from microgravity requirements, has alreadybeen used successfully in industrial research. For example, it has provided the firstvisualisation (appearance and localisation) of combustion-induced oscillations inpower-station gas turbines. Even though it was possible to measure the trend of theseoscillations in terms of pressure waves and noise, it had never previously beenpossible to observe the inducing phenomena. This was due to the fact that leannatural-gas flames are invisible when viewed in front of a 1200˚C chamber wall.

Such observations and measurements are necessary in order to learn how to designburners properly and avoid wasting time on costly trial and error experiments at thecustomer’s site. A diagnostic system based on a solid-state laser of a completely newdesign, with repetition rates up to 2 kHz, is to be used on the International SpaceStation. Doubtless such a system will also find its way into terrestrial applications.

2.3.7.3 Conclusions

Reduced-gravity combustion experiments and modelling have led to a newunderstanding of the basic phenomena in many cases. In particular, the role of thedifferent heat- and mass-transfer parameters in convection, diffusion and radiation isnow much better understood. Consequently, the combustion research community atlarge has never called into question the value or validity of combustion research underreduced-gravity conditions.

However, there are still many inconsistencies to be clarified between results from state-of-the-art modelling and experiments. The problem with microgravity research hasbeen that experiment opportunities have been so limited. Thus the data are alsolimited in number and often too scattered for new theories to be verified in astatistically acceptable manner. On the other hand, in microgravity, combustionresearchers are in a good situation compared to other branches of science. As timescales in combustion are generally short, comparatively cheap and easy accessibledrop towers have proved well suited to, and have been extensively used formicrogravity experiments. With the advent of the International Space Station and itsmore extensive facilities and access, combustion research will receive a major boost.Such a facility with continuous microgravity access will definitely assist in changingthe current situation as regards paucity of data. This fact that the combustionexperiments can still be developed and evaluated at drop towers, before selection andpreparation for space flight begins, will be a significant aid in using the Station and itsfacilities effectively.

ESA’s Topical Teams, as well as the initial projects derived from the Team’s discussions,have proved to be a very suitable means of ensuring focussed, user-driven research.By nature, this kind of research tends to be closer to fundamental research than toapplications, but history has shown that such investment in the fundamentals does

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with research ranging from astrophysics to the laboratory, and where the interactionsbetween the species are mostly due to binary collisions.

By contrast, and by definition, the complex plasma contains the particles (or micro-spheres) as one of the active plasma components, participating in – and evendominating – the plasma physics, both by binary and by collective interactions.

Outstanding examples are the recently discovered liquid and crystalline plasmastates. In the limit of very weak ionisation, for example in the Earth’s atmosphere orin star- and planet-formation regions, other interactions may become dominant. Theseinclude condensation, coagulation, evaporation, and surface chemistry. But there mayalso be important processes such as collisional charging, which may introduceplasma-electromagnetic effects into the system, including possibly quite substantialeffects such as lightning.

The subject of this Section necessarily covers a wide range of topics of broad scientificinterest. Accordingly, the potential and scope of this field is first discussed and anoverview of the diverse research interests is presented. The major fundamentalprocesses that are the subject of current and (especially) future research efforts areintroduced and summarised. This is followed by a discussion of the role thatmicrogravity experimentation plays in these investigations, and the connections withterrestrial laboratory programmes. This naturally leads to a consideration of futureindustrial interests and the requirements for an integrated research effort in microgravity.

2.3.8.2 The Scope and Potential of the Field

In the Introduction, mention was made of some of the general processes occurring(e.g. binary, collective), without being very specific. In order to assess the importanceand potential of this field, it is expedient to take a subject-oriented approach.Accordingly, some of the major research topics and the role played by complex (dusty)plasmas will be briefly summarised, subdivided into two broad areas: first theinterdisciplinary aspects of complex (dusty) plasma science, including its applications,and then the fundamental research into the new liquid and crystalline plasma statesthat were discovered just a few years ago.

- Interdisciplinary Studies

AstrophysicsDusty plasmas are ubiquitous in the field of astrophysics. They are found in interstellarclouds (ionisation fraction smaller than 10-2, dust/gas ratio about 1% by mass), in star-formation regions, protoplanetary disks, circumstellar shells and in expanding, coolingnova and supernova shells.


2.3.8 Complex and Dusty Plasmas

G.E. Morfill & H.M. Thomas


The field of complex and dusty plasmas has been one of the fastest growing researchareas in physics in recent years (Fig. 2.3.8.1).

It was the rapid development of this field that recently prompted the AmericanInstitute of Physics to introduce corresponding identification codes (complex plasmas,dusty plasmas, plasma crystals, PACS 25.52.Zb). The term ‘Complex Plasmas’ waschosen by analogy with fluid physics, where ‘Complex Fluids’ are liquids enriched withsmall nano- or micro-particles, resulting in a rich spectrum of new physical processes– the physics of colloids. Accordingly, ‘Complex Plasmas’ are defined as fully orpartially ionised gases, which are enriched with small nano- or micro-metre-sizedparticles. The inclusion of such particles in the plasma introduces a wealth of newphenomena and exciting physics.

The difference between these complex plasmas and the more historical ‘dustyplasmas’ is that the latter includes the huge field of contaminated (by dust) plasmas,

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Figure 2.3.8.1. Publications in the field of ‘Complex and Dusty Plasmas’ (from A. Mendis)

Figure 2.3.8.3 shows an image of a young star still embedded in its protostellar disc.The object is seen silhouetted against the Orion Nebula in the background. It is thedust that obscures the background light and makes the disc appear dark. Such discsare believed to be the birth places of planets. The dust particles are micron-sized andthe extent of such discs is typically 100 AU.

Solar-System ScienceDusty plasmas are found practically everywhere within the Solar System. The ZodiacalCloud, a tenuous distribution of particles (largely in the 10 to 100 micron range) ismade visible by the reflected sunlight and also through its infrared signature. Theorigin of the zodiacal particles is probably cometary, although some contribution fromthe asteroids and the minor bodies in the Kuiper Belt is also expected. The majorquestions are the source and transport, i.e. the radial evolution. The latter involvesknowledge of the charging by electrons and ions from the solar wind as well as solarUV photons. Collisional and Coulomb drag and – for the very small particles inparticular – radiation pressure and electromagnetic forces are also important.

The planetary rings have been a topic of great interest in dusty plasma physics eversince the detailed measurements by the Voyager missions were made available. Thediscovery of the existence of huge numbers of small micron-sized particles inplanetary magnetospheres was, of course, a surprise. So too were the many significantand unexpected effects that these particles have. As representative examples of thenew discoveries just two are mentioned here: the injection of sub-micron-sizedparticles into Jupiter’s magnetosphere, due to the volcanic activity of the moon Io, andthe dark triangular evolving features found in Saturn’s rings, the ‘spokes’ (Fig. 2.3.8.4).

Major questions in dust-magnetosphere interactions involve the role of: mass loading(particle sputtering, photo-sputtering), impacts (particulate and plasma ejecta),momentum and angular-momentum transfer (ring evolution, instabilities, structureformation), regolith formation, cohesion of particles in a regolith and disagglomerationor electrostatic disruption and levitation, respectively.

There are also novel collective effects. For instance, small dust particles will orbit theirplanet with Keplerian velocity, modified somewhat by electromagnetic and radiationpressure forces. The magnetic field of the planet co-rotates, of course. This implies thatinhomogeneously distributed charged dust particles produce local currents. Thesecurrents have to be closed and this therefore leads to new forms of collective dust-magnetospheric interactions that allow the exchange (ultimately) of gravitational andelectrodynamic energy.

Comets, as already mentioned, are copious suppliers of small dust particles. As theyapproach the Sun, the more volatile materials start to evaporate. This leads to anumber of interesting interactions involving particles, neutrals, the solar wind and


Research has focused upon the basic processes of nucleation – i.e. How are the dustparticles formed? – and on surface chemistry – e.g. What is the role of dust in H2-molecule formation? It includes radiation transfer – in particular the radiative coolingof contracting clouds during star formation. Also included is the charge state: surfacerecombination on dust dominates over gas phase recombination above a certainthreshold density and the cloud may then evolve independently of the magnetic field.

Coagulation studies investigate how particles grow by collision. Do they form fractalaggregates? Dust-gas interactions concern frictional coupling, mass loading ofturbulence, turbulence damping, and soon.

The role of dust is spectacularlyillustrated by two images taken with theHubble Space Telescope (HST). Figure2.3.8.2 shows the Eagle Nebula, which isirradiated by nearby hot stars and slowlyevaporates. However, there are localinhomogeneities – density condensatesthat survive this evaporation processdue to more efficient cooling by the dust.These inhomogeneities are seen ascoherent clumps at the outer perimeter ofthe nebula, and may evolve into the birth-sites of stars.

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Figure 2.3.8.2. HST image of the Eagle Nebula.Note the compact features at the top, whichcould evolve into protostellar clouds (from J. Hester & P. Scowen, Arizona State Univ., HST, NASA)

Figure 2.3.8.3. HST images of a circumstellar disc, which is believed to be the birth regionfor planet formation (from M.J. McCaughrean, MPIA, and C.R. O’Dell, Rice Univ.)

sunlight. In addition, it is believed that comets contain essentially unmodified ‘coldstored’ material from the time of formation of the Solar System. Much of theinformation about comets has come from spectroscopic measurements and, ofcourse, from ESA’s spectacularly successful Giotto mission, confirming the notion of a‘dirty ice ball’ containing mostly light and volatile material. A recent, totallyunexpected result was the discovery that comets can also be detected in X-rays (Fig. 2.3.8.5).

The physics behind the X-ray emission lies in the interaction of the solar wind with theneutral gas and dust. Highly ionised solar-wind particles (in particular ‘heavy’ ions –carbon to iron) collide with the cometary ejecta and cause charge exchange.Recombination then produces photons of several hundred eV, which ultimately lead tothe observed X-ray signatures.

- Atmospheric and Environmental Science

It was mentioned earlier, in the context of impact ionisation, that even very weaklyionised gases – such as the Earth’s atmosphere – can nevertheless exhibit strongelectromagnetic disturbances, such as lightning. This phenomenon occurs duringthunderstorms, sandstorms, as well as in volcanic plumes – in fact everywhere wheregas and dust are present and where free energy of motion exists. The surprise is thata few percent of the available energy in a thunder cloud, for instance, is released vialightning, which makes this non-linear process very efficient.

The physical processes of greatest interest are, as expected, the charge generation, thecharge separation, the charge transport (in particular large-scale separation), theenergy storage and dissipation. Dust, or water droplets, play an important role in allof these processes. This is easy to see, because free electrons would be too mobile toallow electric fields of the required magnitude for electrostatic breakdown to be builtup. Hence, present efforts concentrate on dust (water droplets) as charge generators,as charge separators, and for the charge transport, e.g. size sorting duringsedimentation or in convection cells via inertial effects.

Within the context of Solar System formation, lightning may have played a role too.One particular question of interest here is the charge generation during disruption ofa conglomerate particle. Regarding other environmental issues, one could mentioncluster-ion formation and the role of aerosols in the upper atmosphere, or the recentlydiscovered particle layer in the mesosphere, which may be of man-made origin (a pollution effect) or may be ‘natural’ (e.g. due to meteor ablation). One could alsoinvoke catastrophic events such as huge volcanic eruptions, major meteorite impactsor even the scenario leading to a ‘nuclear winter’. Whatever the issues for research are,they all require a good understanding of the complex interactions involving dustparticles, gases, plasmas, electromagnetic fields and radiation.


Figure 2.3.8.4. Image of Saturn’s rings, including the dark ‘spokes’ (courtesy of NASA)

Figure 2.3.8.5. Contours of the X-ray and extreme-ultraviolet emissions of Comet Hyakutake,superimposed on an optical image. The inner five contour lines show the intensitydistribution of the X-ray emission, observed with the Rosat High-Resolution Imager (HRI),

while the outer threecontours refer to theextreme-ultravioletemission, measuredsimultaneously with theRosat Wide-Field Camera(WFC). The optical imagewas taken during theRosat observations. It isevident that the X-rayemission is comingmainly from the sunwardside of the coma and notfrom the cometarynucleus (courtesy ofK. Dennerl, Max-PlanckInstitut für Extra-terrestrische Physik)

overall charge neutrality and which exchanges momentum and energy with the otherplasma components (ions and electrons). The mobile ions and electrons areredistributed in the electric field around the individual charged microspheres, forminga charge ‘cloud’ of opposite polarity around each particle. This cloud has the effect ofshielding (or neutralising) the microsphere charge over a characteristic distance – theshielding distance. Microspheres can interact with each other only if they approach towithin a few of these shielding distances. If such interactions are frequent, the complexplasma is ‘strongly coupled’. It may even become liquid or crystalline, yet it retains itsplasma character.

- Plasma Crystals

The discovery of crystalline plasma states, the ‘plasma crystals’, was quicklyrecognised as a major advance in plasma physics, although the theoretical possibilityhad been discussed almost ten years earlier. A plasma – normally viewed as the mostdisordered form of matter – that was able to organise itself into a regular structureseemed remarkable at first glance. The promise of unexplored scientific territory andnew physics was very powerful, and it is not surprising, therefore, that a large numberof researchers have taken up the investigation of this new plasma state. Among themain regions of interest in this relatively new field are the following:– Detailed investigation of self-ordering phenomena at the kinetic level for two- and

three-dimensional systems (Fig. 2.3.8.6) – the kinetics of phase transitions.– Investigation of the transition from ‘Coulomb Clusters’, containing small numbers of

microspheres, to large macroscopic crystals – including the energetics of thebinding forces.

– Surface-phenomena investigations at the kinetic level for different systems.– Thermodynamics of plasma crystals, using measurements at the kinetic level, for

both two- and three-dimensional systems.– Three-dimensional structure of lattice defects, defect migration, annealing.– Wave propagation in plasma crystals, compressional and shear waves, dispersion

damping, microscopic physics at critical frequencies (e.g. the Debye frequency).– Shock propagation in plasma crystals, detailed shock structure at the minimum

(inter-particle distance) scale (Fig. 2.3.8.7).– ‘Manufacture’ of glass-like plasma crystals, using suitable mixtures of different

microsphere types, and the investigation of their properties.

These research topics are only a selection of those currently being studied. Each topicwill require many experiments, using sophisticated plasma-chamber designs, imagingand data-analysis systems, before an advanced understanding of the process andbasic principles is achieved.

It is important to note not only that the complex plasma systems are very differentfrom the liquid-colloid (complex liquid) systems, but also that they complement the


- Industrial Processing

Plasma technology is an important branch of industry, involving deposition as well asetching, and active as well as inactive gases. It is used in the manufacture of computerchips and solar cells, in surface treatments and coatings, and it has great potential inthe design and manufacture of complex composite materials, to name but a few of theapplications. Needless to say, the inclusion of nano- or micrometre-sized particles in acontrolled process of manufacturing opens the possibility for new products. Apromising programme involving ‘polymorphous’ (= amorphous plus nanocrystallite)solar cells has been started by the European Union. First results indicate an improve-ment in efficiency by a factor of approximately two compared with amorphous cells,as well as long-term stability.

Other application-related research, in particular controlled particle growth and surfacetreatment, is in progress in various laboratories, with applications ranging frompharmacy to printing.

- Fundamental Research

The discovery in 1994 of liquid and crystalline (complex) plasma states triggered aworldwide avalanche of research activities. Some six years later it is still continuing,with a growing number of researchers engaged in the diverse new science that hasbeen opened up. There are some simple reasons for this continuing and growinginterest:– The strongly coupled liquid and crystalline plasma states can be investigated at the

kinetic level – by direct microscopy of individual particle positions and velocities –which has not been possible before in plasma physics.

– The characteristic plasma time scales are ‘slowed down’ in these systems, due tothe large masses of the microspheres. The microsphere masses are typically ahundred billion times heavier than the plasma ions. This brings the plasmafrequency down from the usual MHz regime into the 10’s of Hz, which are theneasily measurable.

– Control and manipulation of particles is relatively easy using electrostatic, magnetic,mechanical or radiation forces, and hence many active experiments can bedesigned to investigate new phenomena occurring in these systems.

– Many principally different systems can be assembled and investigated –homogeneous, inhomogeneous, anisotropic, coulombic and paramagnetic systemsbeing the most obvious – with different properties of interest for both fundamentaland applied research.

The principal interactions in a complex plasma can be summarised as follows. Themicrospheres become highly charged through collisions with the ions and electrons.They therefore form a separate, massive, plasma component, which contributes to

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research performed with the latter. The main reason lies in the response time scales.Since the neutral and ionised gas has virtually no mass compared with themicrospheres, the damping due to friction between species in complex plasmas istypically 100 000 times smaller than that in complex fluids. This implies, among otherthings, that rapid processes can be investigated using complex plasmas, somethingthat is impossible with complex fluids.

- Liquid Plasmas

Complex plasmas, as mentioned earlier, offer the possibility to observe a liquidpractically at the ‘molecular’ (or kinetic) level. This has already resulted in manylaboratory experimental efforts, since here is a good chance to study thethermodynamics and hydrodynamics from the most basic viewpoint – the motion ofindividual interacting particles. Among the fundamental processes of interest are:– Shear flows and momentum exchange at the kinetic level. Derivation of ‘macroscopic’

fluid properties (e.g. viscosity) from microscopic particle measurements.– Transition from laminar to turbulent flows at the kinetic level. Identification of new

ordering parameters.– Surface physics – microprocesses responsible for surface tension in different systems.– Fluid interfaces at the kinetic level, flows, perturbations, instabilities.– Impacts between liquid-plasma bubbles, including the full kinetics and energetics of

the momentum transfer and energy dissipation.– Study of convection cells at the kinetic level, self-organisation and structure

formation (Fig. 2.3.8.8).– Kinetics of guided flows (constriction, obstacles, redirection) to investigate inertial

terms, for instance.– Investigation of the response to oscillations, global mode excitations, etc.

Again, these research topics are just some examples of the current research. There aremany more projects in preparation worldwide, particularly in the areas of activeexperiments, and it is practically certain that the forthcoming research will yield newquestions that require even further studies. It therefore seems reasonable to assumethat ‘liquid plasmas’ will contribute significantly to the detailed understanding of arange of nonlinear problems in fluid physics.

- Some Basic Physics Issues

There are several principal issues that have not yet been resolved, even after manydecades of research. Complex plasma investigations may be able to makecontributions here and initiate further advances. Among the currently unresolvedquestions are the following:


Figure 2.3.8.6. Phase transition from crystalline to disordered states of a strongly coupledcomplex plasma (from Thomas & Morfill 1996, Nature, 379, 806). The phases shown are:(a) crystalline, (b) co-existence of crystalline ‘islands’ and liquid states, (c) a vibrationalphase that exhibits large-scale order and excited particles, and (d) disordered state

Figure 2.3.8.7. Mach cones observed in a two-dimensional plasma crystal. The complexstructure resulting from inter-lattice forces (compression, rarefaction) is normally notdiscernible in macroscopic systems, where the scales exceed the inter-particle distancesby many orders of magnitude. The figure shows particle velocity (grey-shaded) as well asparticle positions (a snapshot), illustrating the relationship between shock structure andlattice separation (adapted from Samsonov et al. 1999, Phys. Rev. Lett., 83, 18, 3649)

– Parasitic charge depletion, caused by high concentrations of particles in a plasma,is a topic of fundamental interest. It includes the spatial charge distribution in aparticle cloud – in particular, the transition to a solid, where the charge is located atthe surface.

– Dust–gas friction for single particles can be described quite well with, for example,the Epstein drag law (provided the conditions apply). For particle clouds, shielding(from the flow) may become important – the Bernoulli effect – so that themomentum exchange with the gas is less effective. This process is important inastrophysics, atmospheric physics, combustion, pollution control, etc.

– The physics of granular media is observable (usually) only in terms of surfaceeffects. Complex plasmas provide special interacting ‘granules’ – pseudo-particleswith a size governed by the shielding length, where the ‘visible’ particle inside maybe substantially smaller. This allows (in principle) the analysis of granular media inthree dimensions – subject of course to the limitations imposed by the forces ofinteraction.

– Radiation pressure acting on single particles of different composition and structure(e.g. conglomerates) can be investigated in detail. This is of importance inastrophysics, but possibly also for industrial applications. Wavelength dependenciescan be studied using different laser light sources.

– Radiation pressure acting on particle clouds is another interesting topic, which isagain of wide interest wherever particle inhomogeneities occur.

This list of process-oriented research is by no means exhaustive. Even so, it illustratesthe enormous potential of the field and the new possibilities for making precisequantitative studies of different effects that have been opened up. It also highlightssome of the obvious uses of the new knowledge to be gained.

2.3.8.3 The Microgravity Requirement

It has been mentioned already that the individual particles of the micro-particlecomponent of complex plasmas are typically one hundred billion times heavier thanthe plasma ions. This implies that gravity is an important force and has an importantinfluence on the behaviour of the system. For many research and application purposesthis is useful and desirable; on the other hand, for a large number of topics it is not.The latter are typically of the following generic type:– Investigations into fundamental properties of complex plasmas.– Investigations where natural phenomena in space are simulated experimentally.– Investigations involving small changes in energy levels or surface properties.– Three-dimensional systems.

As can easily be seen, in some ways practically all of the research topics mentioned inSection 2.3.8.2 are involved. Consequently, in order to avoid repetition, it is simplypointed out that by the very nature of this research – operating with particles that are


– Charging of objects in a plasma is an old topic, which is still the subject of intensiveresearch. New approaches (e.g. binary collision experiments) have already beenvery valuable (Fig. 2.3.8.9). New activities could involve the investigation of differentplasmas including composition and streaming as well as different particle shapesand ultraviolet radiation.

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Figure 2.3.8.8. Convection patterns induced in strongly coupled complex patterns (fromLaw et al. 1998, Phys. Rev. Lett. 80, 19, 4189)

Figure 2.3.8.9. Electrostatic potential around an isolated spherical particle in a plasma,derived from collision experiments for three different plasma conditions. The solid line isthe Debye-Hückel potential, i.e. the theoretically predicted form. Discrepancies from thistheory are predicted to occur at larger distances (possible attractive potentials) and atsmall distances (from Konopka et al. 2000, Phys. Rev. Lett., 84, 891)

already been taken already, as is illustrated by two results. The first example (Fig.2.3.8.10) comes from the Plasma-Kristall-Experiment (PKE). The measurements weremade on a sounding rocket and show stable regions as well as rotating cells. Interestfocuses on the sharp boundaries of the system (in particular the inner ‘void’), theinterface between stable and rotating layers, the differential shear motion, etc. Theseaspects will have to be among the topics for future experiments, which will beperformed on the International Space Station. They are one of the first natural-scienceexperiments to be conducted on the ISS in a joint German/Russian research co-operation, and are an important step for the development of a possible InternationalMicrogravity Plasma Facility.

The second example (Fig. 2.3.8.11) comes from an experiment designed to measurecoagulation of microscopic particles under astrophysical (microgravity) conditions –the ‘Cosmic Dust Aggregation Experiment’ (CODAG) – which was flown on SpaceShuttle mission STS-95 in October 1995. Mono-disperse spherical SiO2 (glass) dustgrains were dispersed into a neutral gas (T = 300 K, P = 0.75 mbar) and allowed tocoagulate.

The particles appear to cluster in long strings, with the conglomerates appearingneedle-shaped. This result agrees quite well with astrophysical observations that oftenshow that starlight that has passed through a certain column density of gas and duston its way to our Solar System is polarised. The polarisation is interpreted as being dueto the alignment of needle-shaped dust particles with the magnetic field. If the needleshapes are caused by coagulation, as the CODAG data suggest, then this informationcan be used to determine collision rates and hence the source and age of the particlesin interstellar clouds.


very heavy relative to the plasma ions and electrons – microgravity is likely to be animportant requirement for many study topics.

Another issue is how long, how stable, and how small, should the ‘micro’-gravityconditions have to be? The possibilities for continuous reduced gravity are:– Drop towers: ~ 5 seconds– Aircraft: ~ 20 seconds– Rockets: ~ 6 minutes– Space Station: ~ hours – months.

The quality and stability of the reduced-gravity conditions vary as well, but it is theextent and continuity of the available experimentation time that is the dominantfactor. It is clear that most of the research summarised in Section 2.3.8.2 requires longperiods of microgravity for careful experimental work, leading to the followingrequirements:

(i) A Research Facility on the Space Station, which can be reconfigured to suitindividual experimental requirements. It should be flexible, through being

computer-operated, have variable experiment control, and contain an adequatediagnostics and data-handling capability. This is the most important requirement.Estimates of the total operating time for such a facility, based on the researchprogrammes discussed earlier, are in excess of 10 years.

(ii) A Complementary Laboratory Development Programme, which works in two ways– firstly, to develop new hardware for space-operated science platforms, andsecondly to transfer knowhow obtained from microgravity research back toterrestrial laboratories. This can then be used to improve basic knowledge orprovide possible applications.

(iii) Test Facilities on Parabolic-flight Aircraft, to pre-calibrate and test newly developedhardware for the Space Station in a reduced-gravity environment. Experience hasshown that such tests are absolutely necessary in a research area that deals withhighly nonlinear processes, where in many cases the outcome (even of simpleissues) cannot be predicted.

(iv) Provision of Rocket Flights, for systems that require a longer uninterruptedreduced-gravity period for testing and even preliminary results.

(v) Adequate Manpower Support, for data handling, archiving and data distributionand, most important of all, for understanding the science.

In short, the requirement for this new and rapidly growing field of Complex Plasmas isan integrated space and laboratory programme. The first steps in this direction have

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Figure 2.3.8.10. Microsphere distribution observed in the first microgravity experiments incomplex plasmas using an RF plasma chamber. Note the sharp boundary towards thecentral ‘void’, the convective-type outer envelope, and the steady near-crystalline portionsof the system (from Morfill et al. 1999, Phys. Rev. Lett. 83, 1598)

2.3.8.4 Conclusion

In the foregoing, the huge diversity of the research in the field of complex plasmas andits enormous potential has been outlined. The research includes the physics ofstrongly coupled plasmas (liquid and crystalline states) and the microscopic analysis– on a scale of ‘crystal lattice’ or individual-particle separations – of phenomena suchas the transition to turbulence, momentum transfer in shear flows, shock structure,wave propagation, the physics of interfaces, etc. All of these can be observed on akinetic level for the first time. It extends to astrophysical, environmental and SolarSystem phenomena, which are directly relevant to the understanding of the formationof planets, comets and asteroids, as well as to pollution problems.

The basic knowledge obtained from this research is also expected to yield significantbenefits for industrial purposes. Plasma technology and colloid technology are thebasis for important branches of industrial production. The combination – plasmacolloid technology – has great potential as a future manufacturing process, as itcombines speed, control and precision. This might benefit in particular the area ofcomplex ‘designer’ materials.

Looking to the future, an integrated research programme, which uses a multi-purpose‘International Microgravity Plasma Facility’ (IMPF) and also a facility to study the‘Interactions of Cosmic and Atmospheric Particle Systems’ (ICAPS), is needed toprovide continuous research opportunities in space on the ISS. This should be alliedwith appropriate terrestrial laboratory programmes that include transfer of knowhowto industry. These are the next logical steps for this growing and important field ofresearch and their implementation will ensure the continuing growth in Europe of thebasic understanding of these complex processes and will provide the link to exploitpossible applications.

Further Reading

Bertran E., Sharma S.N, Viera G., Costa J., St’ahel P. & Roca i Cabarocas P. 1998, Effectof the nanoparticles on the structure and crystallization of amorphous silicon thinfilms produced by RF glow discharge, J. Mater. Res., 13, pp. 2476 – 2479.

Blum J. 2000, Laboratory experiments on preplanetary dust aggregation, SpaceScience Rev., 92, pp. 265 – 278.

Cuzzi J.N., Dobrovolskis A.R. & Hogan R.C. 1996, Turbulence, Chondrules, andPlanetesimals. In: Chondrules and the Protoplanetary Disk (Eds. R. Hewins, R. Jones &E.R.D. Scott), Cambridge Univ. Press, Cambridge.


Figure 2.3.8.11. Coagulated particles observed under microgravity conditions in theCODAG experiment (from Blum et al. 1999, Meas. Sci. Technol., 10, 836)

camera 1 camera 250 µm

2.3.9 Vibrational Phenomena in Fluids and Granular Matter

D. Beysens


Vibrations in matter act on inhomogeneities, which generally tends to direct themperpendicular to the acceleration direction. The inhomogeneities can be due to thegranular structure of the matter itself, acting as if it is an assembly of hard beads; they can be density inhomogeneities, such as those induced in a simple fluid bytemperature gradients; or they can be created by the coexistence of two phases (e.g.liquid and vapour). In a sense, vibrations can play the role of an artificial gravity,inducing flows, structuring the gas/liquid interfaces, and eventually helping to controlfluids when in space.

The phenomena associated with such vibrations form a rich collection of situations,whose diversity has yet to be fully investigated. It is, however, a subject ofconsiderable importance, not only for discovering new phenomena, but also, withinthe space context, for evaluating the effect of the unavoidable vibrations occurring inspacecraft structures. These may, in some cases, considerably perturb fluid andmaterial-science experiments and are likely to be of concern for the InternationalSpace Station.

Investigations into the behaviour of inhomogeneous materials submitted to vibrationsunder microgravity conditions have started only recently. However, a certain numberof significant results have already been obtained and these are reviewed below. Theeffects in fluids are first reported. There, the critical point plays an important role, sincesimply by inducing a change in the proximity to the critical point the properties canbe modified in a scaled, universal way. Following that discussion, the effect ofvibrations on granular matter are analysed.

2.3.9.2 Vibration Effects in Fluids and Near-Critical Fluids

- Why Study Vibrating Fluids under Microgravity?

Vibrations applied to mechanical systems can cause destabilisation or stabilisation,depending upon the characteristic features of the vibrations, i.e. the frequency, or theangular frequency, the amplitude, and the direction of vibration. Many equilibrium andnon-equilibrium phenomena can be affected by the presence of high-frequency vibrations.


Goertz C.K., Morfill G., Ip W., Grün E. & Havnes O. 1986, Electromagnetic AngularMomentum Transport in Saturn’s Rings, Nature, 320, p.141.

Grün E., Morfill G. & Mendis D. 1984, Dust-Magnetosphere Interactions in PlanetaryRings (Eds. A. Brahic & R. Greenberg), pp. 275 – 333.

Ikezi H. 1986, Coulomb solid of small particles in plasmas, Phys. Fluids, 29, 6, pp. 1764 – 1766.

Lin I, Wen-Tau Juan, Chih-Hui Chiang & Chu J. H. 1996, Microscopic Particle Motions inStrongly Coupled Dusty Plasmas, Science, 272, pp. 1626 – 1628.

Morfill G. 1985, Physics and Chemistry in the Primitive Solar Nebula. In: Birth andInfancy of Stars (Eds. R. Lucas & A. Omont), pp. 693 – 792.

Morfill G., Spruit H. & Levy E.H. 1993, Physical processes and conditions associatedwith the formation of protoplanetary disks. In: Protostars and Planets III (Eds. E.H. Levy& J.I. Lunine), University of Arizona Press, Tucson and London, pp. 939 – 978.

Poppe T., Blum J. & Henning T. 2000, Analogous experiments on the stickiness ofmicron-sized preplanetary dust, Astrophys. J., 533, pp. 454 – 471.

Thomas H., Morfill G.E., Demmel V., Goree J., Feuerbacher B. & Möhlmann D. 1994,Plasma Crystal: Coulomb Crystallization in a Dusty Plasma, Phys. Rev. Lett., 73, pp. 652 – 655.

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The only available results in microgravity are preliminary data gathered in a sounding-rocket experiment. Three samples of different gas volume-fractions and distances from thecritical point, were vibrated at different amplitudes and frequencies ranging from 0.1 to5 mm and 0.1 to 60 Hz. Although the initial state of the sample was a vapour dropemulsion or a unique drop, the final state was the same: vapour and gas phases formingalternate layers perpendicular to the acceleration vector (Fig. 2.3.9.1c). The instabilitydevelops as liquid fingers from the cell walls and then coalesces with the droplets in thebulk and/or with the fingers that have grown from the opposite side.

These observations suggest that, under some circumstances, a periodic excitation canact as a kind of artificial gravity to localise the liquid and vapour phases perpendicularto it. This occurs irrespective of the initial configuration (emulsion of vapour dropletsor a unique vapour drop). These are preliminary studies of the phenomenology of one-or two-phase fluids, subjected to oscillatory accelerations under microgravity. Atpresent, there is little theoretical understanding of these phenomena.

- Vibrational Thermal Effects

Consider a planar fluid layer under a vibrational acceleration field, which is subjectedto a thermal gradient by heating from below. Convection is able to start when thebuoyancy effect of the hot lower density fluid can overcome the energy dissipationdue to viscous drag and heat diffusion (this is the well-known Rayleigh-Benardinstability). As the temperature of the fluid gets closer to the critical temperature, thedensity change due to heating is increasingly important and the fluid becomesextremely sensitive to the vibration-induced acceleration.

Measurements of flow velocities performed on the Mir station in CO2 and in SF6,confirm this expectation. A heat flux was sent into the fluid from a point-like source(thermistor). Depending on the oscillation velocity, two regimes of heat propagationwere observed: (i) at low frequency, heat is convected during one oscillation period to


The periodic acceleration due to vibrations can have a marked influence on thebehaviour of fluids near to their critical point. Different phenomena are presentlyunder consideration, including induced thermal instabilities, analogous toviscosity/diffusion moderated convection, and ordering of the gas/liquid interfacebelow the critical point. The question of how the acceleration can be transmitted to the compressible fluid through a mechanical boundary layer will not be discussed here. It is simply assumed that the fluid is submitted in bulk to a periodicacceleration.

A number of theoretical aspects have been considered in some detail by Russianscientists. They conclude that the suppression of the uniform steady gravity field ismandatory in order to evaluate the phenomena induced by vibration.

- Interface Deformation and Localisation

On Earth, the usual effect of vertical vibrations in a fluid is to modulate the localeffective gravity force, via the time-dependent acceleration applied to the system.Under microgravity, the response can be markedly different and concerns not only theshape and localisation of the gas/liquid interfaces, but also the evolution andmorphology of the drop pattern during a phase transition.

A plane liquid-vapour layer, vertically vibrated parallel to gravity, displays two differentregimes. Far from the critical point, a square wave-pattern deformation is formed. At atemperature T0 close to the critical temperature (Tc – T0 ≈ 20 mK for CO2), a transitionoccurs to a new pattern configuration of lines. This transition is due to the increase indissipation near the critical point. This is a rather unique example of strong couplingbetween two different critical-point phenomena. These are the critical point ofinterface instability and the thermal critical point of the liquid–vapour phasetransition.

When, in gravity, the acceleration is parallel to the interface, an instability is observedwith the interface modulated as a ‘frozen’ roll wave pattern (Fig. 2.3.9.1b). Thisphenomenon corresponds to the formation of waves on the sea under the influence ofthe wind. As yet, it has been only poorly investigated for the present case, where the‘wind’, i.e. the gas phase, exhibits a periodic velocity relative to the ‘sea’, here theliquid. The instability mechanism is due to the relative motion of two fluids induced byvibration. The perturbation becomes unstable if the velocity is larger than a thresholdvelocity, determined by the gas–liquid surface tension and the densities of the liquidand vapour. This destabilisation is due to the increasing effect of the Bernoulli-typepressure, arising from the velocity difference between gas and liquid. The experimentsconducted recently are consistent with this model, with the velocity as the relevantparameter governing the instability.

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Figure 2.3.9.1. Gas-liquid phases, which show up under 1g as a vapour phase above theliquid phase separated by a flat meniscus, and under 0g as a vapour bubble surroundedby a liquid phase (a), can order in a different way when submitted to vibration. Illustratedin (b) are frozen waves under 1g, and in (c) gas-liquid ordering under 0g (Mini-Texus-5,February 1998) (from Beysens et al. 1998, Micrograv. Sci. & Techn., 11, 113)

- Phase Transition in a Granular Gas

The first experiment with slightly dissipative granular media was carried out onparabolic low-gravity flights, on board CNES’s Caravelle aircraft in 1991. It tested thePV = nRT law of a perfect gas, using a collection of macroscopic stainless-steelspheres. Its purpose was mainly information gathering and showed reasonableagreement between pressure and temperature equivalence, and with the Boltzmannstatistics.

The first experimental evidence of a phase transition in a granular gas was providedby a Mini-Texus-5 sounding-rocket experiment in 1998. Although this collapse waspredicted by numerous theoretical and numerical studies, it had never been observed,even in two dimensions. It was found that the formation of a dense cluster of particlesin a ‘liquid’ or cluster regime (low velocity, small free mean path) in equilibrium with afraction of the particles in a ‘gaseous’ regime (high velocity, large free mean path)occurred above a well-defined threshold in particle number density (Fig. 2.3.9.3). Theobservation of such a dissipative collapse has important consequences inastrophysics, particularly for the analysis of the formation of planetary rings (see alsoSection 2.3.8).

The difference between the two kinetic regimes, homogeneous and clustered, is alsoapparent in the pressure signals. In the dilute case, the pressure of the granular gasscales like the 3/2 power of the vibration velocity. This is quite surprising, since the basicargument predicts a power of 2. So it seems that this result can only be explained bysome special dependence of the collision-restitution coefficient upon velocity.


form symmetrical hot layers perpendicular to the vibration (configurationhot–cold–hot, Fig. 2.3.9.2b); and (ii) at high frequency, heat is convected by convectionrolls perpendicular to the direction of oscillation (opposite configuration,cold–hot–cold, Fig. 2.3.9.2c).

2.3.9.3 Vibrations in Granular Matter

Although studied for several centuries due to their various industrial applications,granular media have recently received renewed attention from physicists. Granularmedia indeed exhibit a wide range of behaviours – solid-like, gas-like and liquid-like –depending upon the dynamic coupling of the particles with the surrounding mediaand the intensity of the mechanical excitation. Dynamic decoupling between theparticles and the surrounding media is achieved by using a low-pressure, low-densityfluid, such as air at atmospheric pressure, or even vacuum. In such a fluid, the solidparticles can be considered as isolated bodies between each collision, and one of themost interesting properties is the dissipative nature of the particle–particleinteractions (inelastic collisions). The usual techniques and results of statisticalmechanics can then be used to analyse the thermo-statistics of a dissipative gas.

- Low Gravity for Granular Media Studies

From an experimental point of view, in order to study its properties in a steady state,it is necessary to bring to the gas a steady amount of kinetic energy that balances thedissipative losses. Mechanical vibrations are a common way to keep the temperatureof such a macroscopic gas constant. On Earth, the energy of the particles depends ontheir relative height, and stratification occurs at all levels of vibration. Observation ofa ‘phase transition’ in granular media is therefore uncertain, and the experimentaltests of theoretical predictions problematic. Although it is possible to immerse theparticles in a liquid of comparable density, this situation induces strong dynamiccoupling between the particles and the fluid, leading to liquid-like behaviour of thegranular media. In contrast, a low-gravity environment eliminates stratification, evenat high density ratios, and produces an effectively isolated gas of particles.

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Figure 2.3.9.2. The spreading of the hot boundary layer during the heating of the thermistor(Th1, supported by a thread): (a) without vibration (hot region underlined in white); (b) underlow-frequency vibration; and (c) under high-frequency vibration, where convection rolls form(ALICE on Mir, 1999)

Figure 2.3.9.3. ‘Gas–liquid’transition for granular mattersubjected to vibration undermicrogravity conditions (ESA Mini-Texus-5, 1998): (a) gas behaviour(G); (b) cluster behaviour (C). In themost dilute case (a), the particlesmove erratically and theirdistribution is roughlyhomogeneous in space. In thedenser cases (b), a ‘motionless’dense cluster (in black, C) issurrounded by regions of lowerparticle density (from Falcon et al.1999, Phys. Rev. Lett., 83, 440)

- Granular Matter

An intensive study of dissipative collapse is the natural goal of the research programmeon granular matter, in order to build up an experimental phase diagram of granularmatter under vibrations. From a thermodynamic point of view, vibrations are used tomaintain the kinetic energy of the gas, whereas the granular pressure is measured bysimple sensors and the temperature evaluated via the velocity of the particles.

For this purpose, systematic experiments have to be conducted to determine thenumber-density threshold where the collapse occurs. The influence of the couplingbetween the surrounding fluid through viscosity or compressibility also needs to bestudied in detail, as should the perturbing effect of electrostatic forces. In this sense, anexhaustive programme of ground-based experiments combining various fluids, amongthem supercritical fluids and granular media, should be carried out in order to extend therecent theoretical and experimental results on fluidised granular media. An extendedrange of excitation intensities and longer experiments should allow the kinetics of thecollapse process to be investigated. Improvements in the detection of the particles andlarger sample cells should also permit the formation of multiple clusters to be detectedand their coalescence studied. In parallel, the pressure fluctuations should be measuredand modelled, in order to determine the free energy of the granular matter.

Another subject of interest is the segregation mechanism of binary mixtures (particlesspecies of different sizes, shapes or densities). On Earth, segregation is frequentlyobserved, but there is no unified theory for this phenomenon. Even the pertinence of thedescription in terms of minimisation of interaction energy is still an open question. This‘hot’ scientific problem is presently the object of a few microgravity experiments fundedby NASA and the Japanese Space Agency, in an industrial context. Since the NASAexperiment consists of shearing a binary granular mixture in low gravity, the experiments proposed here, involving vibrating a granular medium, arecomplementary in nature.

Further Reading

Falcon E., Wunenburger R., Evesque P., Fauvé S., Chabot C., Garrabos Y. & Beysens D.1999, Building Theory on Sand, Science, 285, p. 521.

Falcon E., Wunenburger R., Evesque P., Fauvé S., Chabot C., Garrabos Y. & Beysens D.1999, Cluster Formation in a Granular Medium Fluidised by Vibrations in Low Gravity,Phys. Rev. Lett., 83, p. 440.

Gershuni G.Z. & Lyubimov D.V. 1998, Thermal Vibrational Convection, John Wiley &Sons, New York.


2.3.9.4 Prospects for the ISS

It is a remarkable fact that the effect of vibrations on inhomogeneous media undermicrogravity conditions is largely unknown. Detailed data on this phenomenon arestill lacking. Non-linear vibrations may induce new forces, which may help to controlthe flow of fluids in space, and that in turn can be used for the phase separation ofheterogeneous media in the space environment. It seems very likely that this studywill lead to new processes in applied science and technology.

In the future, the members of the ESA Topical Team on ‘Vibrational Phenomena’ propose toenlarge the preliminary investigations that were performed with fluids and granularmaterials. What is basically needed is a vibration set-up whose amplitude ranges from 0.1 to50 mm and frequency from 0.1 to 100 Hz, with maximum acceleration in the range 1 – 10 g.

- Fluids and Near-Critical Fluids

The first objective is to understand the coupling between heat transfer and high-frequency vibration. Since no buoyancy forces exist in microgravity, the only possibleheat-transfer mechanism in the absence of vibration is thermal diffusion (and thePiston Effect for near-critical fluids). A well-controlled method for investigating thechange in the heat-transfer mechanism is to use a single-phase fluid under a thermalgradient and to submit it to controlled oscillatory acceleration. The main effect of high-frequency vibrations would be to restore convection, as reported above in Figure2.3.9.2, thereby behaving as if they induce an artificial gravity.

Concerning the behaviour of a two-phase fluid, the main scientific objectives are tounderstand the interface deformation and ordering/organisation mechanisms, inparticular the roles of density ratio and interfacial tension, and in addition todetermine the coalescence laws of dispersed two-phase fluids, when submitted tosuch oscillating accelerations. A goal of this study will be to achieve sufficientknowledge of the ordering mechanism to be able to control and predict thelocalisation of the fluid interfaces under microgravity conditions.

Another objective is to understand how vibrations can induce ordering mechanisms in adispersed system, such as a metastable gas–liquid dispersion. It should be interesting toanalyse the effect of alternating accelerations on phase separation in the same way asthe effect of shear on phase-separation kinetics, i.e. in terms of the anisotropic law ofdomain growth, domain deformation, growth acceleration and final equilibrium state.

The understanding of these effects is important in the control of gas/liquid interfacesand the enhancement of heat transfer in microgravity. It will also furnish informationon the spurious and destabilising effects of ISS structure vibrations on the numerousexperiments using heterogeneous media.

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The second advantage stems from the fact that space constitutes a unique laboratoryin which to test fundamental physical laws with great precision. It is well known thata conflict exists today between general relativity, which describes classical gravitationwell, and quantum mechanics, which describes microscopic phenomena well. As yet,there is no satisfactory quantum theory of gravitation. Theoreticians are still seekingto unify all four fundamental interactions of nature into a single theory.

In space, the Equivalence Principle (the universality of free fall), which forms the basisof Einstein’s general-relativity theory, can be tested with orders-of-magnitudeimprovement over ground-based experiments. Similarly, the famous gravitational red-shift effect (whereby a clock in Earth orbit is seen to run faster by an Earth-basedobserver!) can be tested with unprecedented accuracy by comparing ultra-stableclocks orbiting around the Earth with companion clocks on Earth. Other fundamentalpredictions of general relativity and of modern physical theories can be tested in spaceand will constitute a crucial search for new interactions or new forces.

These two aspects will be illustrated here using the specific example of atomic clocks.Firstly, the main methods for cooling atoms to very low temperatures, i.e. less thanone millionth of a degree above absolute zero, will be reviewed. The principle of anatomic clock is then introduced and the advantages of using space are discussed. Thecurrent PHARAO and ACES projects, which will fly on the ISS in 2005, are thendescribed. Finally, some perspectives for cold atoms for other future space missionsare outlined.

2.3.10.2 Cooling Methods

- Laser Cooling

In laser-cooling experiments, photons are used to exert forces on the atoms. When anatom absorbs or emits a photon its speed changes, so that the total (atom + photon)momentum is conserved. This change is called the recoil velocity and is usually verysmall. For caesium atoms illuminated with light at a wavelength of 0.852 µm, therecoil velocity is 3.5 mm/s. However, the atom is able to absorb and emit at typically10 million times per second, so that the net force that a laser beam can exert on anatom can be very large. Typically, the force can exceed that of gravity by five orders ofmagnitude. This force exerted by a laser beam is called the ‘radiation pressure’.

Cooling a gas of atoms consists of reducing the thermal fluctuations in the atoms’velocity around their mean velocity. The mean velocity can be zero, in which case thegas is at rest in the laboratory. In the case of an atomic beam, the mean velocity is notzero and can be adjusted. Several laser cooling mechanisms have been invented andthe simplest of them is called ‘Doppler cooling’, because it relies on the Doppler effect.


2.3.10 Cold Atoms in Space and Atomic Clocks

C. Salomon


The research field of atom manipulation by the use of laser light has experiencedconsiderable growth over the last 20 years. From the initial demonstrationexperiments in the early 1980s, it has evolved into a mature domain with a wealth ofnew applications, as demonstrated by the awarding of the 1997 Nobel Prize forPhysics to S. Chu, C. Cohen-Tannoudji and W. Phillips. Applications such as ultra-stableclocks, matter-wave interferometers, Bose-Einstein condensation and atom lasershave developed rapidly, and it is now conceivable to fly such systems in space.

For cold atoms, space brings two major advantages. Firstly, it offers the state ofweightlessness. Atoms can now be cooled down to such low temperatures that theEarth’s gravitational force represents a major perturbation to their motion. Take, forinstance, a gaseous ensemble of rubidium atoms, which is cooled in an ‘atom trap’ toa temperature sufficiently low that a Bose-Einstein condensation occurs (Fig. 2.3.10.1).

In this spectacular quantum phenomenon, nearly all of the atoms accumulate in thelowest energy state of the trap, and theyall behave in exactly the same way. Inthis system, the atoms have, on average,a speed of barely 30 µm/sec. On Earth,however, as soon as the trap is switchedoff the atoms acquire a speed of 1 m/sunder the effect of gravitationalacceleration, and they do so in just onetenth of a second. This exceeds theirinitial velocity by a factor 33 000 ! In onesecond, these atoms will have droppedby 5 m and have usually hit the bottomof the vacuum chamber in which theywere cooled. In space, this problemdisappears because of the microgravityconditions. The atoms can then beretained within the observation volumefor periods ranging from several secondsto tens of seconds.

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Figure 2.3.10.1. An atom laser: atoms areextracted from a cold rubidium gas (left) orfrom a Bose-Einstein condensate (right). Theintense, low-divergence, coherent atomic beamis affected by gravity (courtesy of MunichUniversity)

a suitable choice of the laser-beam polarisations, a restoring force can be created thatattracts the atoms towards the point where the magnetic field is zero, at the centre ofthe laser beams. This force accumulates the atoms in a ball of a few cubic millimetres(Fig. 2.3.10.2b) at a temperature of a few micro Kelvin.

- Evaporative Cooling

Cooling of dilute gases has been pushed even further by a totally different technique,well known to everybody who tries to drink a cup of coffee that is too hot! You blowair on it! This cooling is not due to the difference in temperature between the air andthe coffee, but to the evaporation of the coffee that is enhanced by blowing on it.Removing a molecule from the liquid takes up energy that is extracted from theremaining liquid. The liquid then cools down.

The cooling process for atoms is the same. The atoms are confined in a magnetic trap,in which they oscillate and collide with other trapped atoms. The magnetic trap has abowl-shaped potential energy form that possesses a minimum and has a ‘rim’ at afinite potential-energy ‘height’. If the ‘height’ of the rim is reduced to a value thatslightly exceeds the average kinetic energy of the atoms, the fastest atoms will escapefrom the bowl. The remaining atoms then re-thermalise through collisions to atemperature that is lower than the initial temperature. It can be shown that, despitethe loss of atoms in this process, the density of atoms at the centre of the trapincreases and the temperature continuously decreases. Typically, a factor of tendecrease in atom number brings a factor of ten reduction in temperature. Using thismethod, in 1995 the group of E. Cornell and C. Wieman at JILA and the University ofColorado (USA) succeeded in producing a very peculiar new state of matter: a Bose-Einstein condensate of rubidium atoms.

2.3.10.3 Bose-Einstein Condensation and Atom Lasers

According to quantum mechanics, one can associate a wave with each particle ofmatter. The period of this wave is inversely proportional to the particle’s velocity v, andis called the ‘de Broglie wavelength’: λDB = h/Mv, where h is Planck’s constant and Mthe mass of the particle. When the velocity of the particle becomes very low, as isachieved with laser and evaporative cooling methods, the de Broglie wavelength canexceed 1 µm, which is the typical wavelength of visible light.

In 1925, inspired by the work of the young physicist S. Bose, A. Einstein predicted anextraordinary property for a gas of identical particles at low temperature and highdensity in a confining box. This was that, when the mean separation between theparticles becomes of the order of their de Broglie wavelength, a large fraction of theatoms will condense into the lowest energy state of the system. This is the state withzero velocity, if the size of the box becomes arbitrarily large. In the magnetic trap of


It was proposed by T. Hänsch and A. Schawlow, in 1975. The atoms are illuminated bytwo counter-propagating lasers of equal intensity and the same frequency νL (Fig.2.3.10.2a).

The frequency of the lasers is chosen to be slightly below the frequency at which theatoms absorb when they are at rest. When an atom moves, it sees the frequency of thelaser propagating against its motion as up-shifted (just as the sound of a police carcoming towards you has a higher pitch) and it absorbs photons from this wave.Conversely, the atom sees the laser beam that propagates in the same direction witha frequency that is down-shifted (more red). The atom then absorbs many lessphotons from this beam. Thus the net misbalance between the two radiationpressures leads to a slowing of the atom.

This mechanism is very efficient. When the laser beams are oriented along the threedirections of space, the atoms are rapidly cooled and viscously confined within thelaser beams, forming an optical ‘molasses’. The average speed of the atoms is thendamped to about 10 cm/s. At this stage an even more efficient cooling mechanismtakes over. It lowers the speed to a mere 1 cm/s, corresponding to a temperature ofabout 1 µK.

An interesting variant of the optical molasses combines the previous cooling forcewith a trapping force. It is called a ‘magneto-optical trap’ and it is the workhorse incold-atom manipulation. In this process, an inhomogeneous magnetic field, created bytwo coils located on each side of the experimental cell, is added to the molasses. With

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Figure 2.3.10.2. (a) The principle of lasercooling. Two counter-propagating laser beamsexert a radiation pressure force on an atom.When the atom moves, because of the Dopplereffect, the laser that opposes the atom’svelocity has a larger radiation pressure thanthe beam that co-propagates with the atom.Therefore the atom’s velocity is damped. If thisbeam configuration is used along threeorthogonal directions in space, all threevelocity components are damped. This is anoptical ‘molasses’, in which atoms areviscously confined

(b) A magneto-optical trap. In this glass cell, thered ball at centre is the fluorescence of a billionatoms, cooled and trapped by six laser beams.The two white rings hold the magnetic-fieldcoils

clocks. As illustrated in Figure 2.3.10.4, in an atomic clock a very stable radio-frequency source is used to probe a transition between two energy levels in an atom.Since 1967, the primary time standard relies upon caesium atoms and the atomictransition is between two hyperfine states of the electronic ground-state.

By definition, the frequency of this transition is νo = 9 192 631 770 Hz. When theradio frequency is scanned around the atomic transition, it excites the atoms and aresonance curve is obtained. The narrower the resonance curve, the more accurate thefrequency determination, and hence the better will be the clock.

In practice, the radio frequency is electronically locked to the peak of the resonance.As the width of this resonance is simply the inverse of the time taken by the atoms tocross the radio-frequency interaction zone, slow atoms will allow longer transit timesand hence a narrower width. Commercial clocks use atoms travelling at an averagespeed of 100 m/s. Laser-cooled caesium atoms move at a speed of 1 cm/s.Consequently, the gain in interaction time for a fixed device length could reach a factorof 10 000! Because of the Earth’s gravity, this gain is ‘only’ 100, and one uses afountain geometry as shown in Figure 2.3.10.5. In space, a further factor of 10 isexpected.


the JILA experiment, about 100 000 rubidium atoms condensed into the lowest stateof the trap, forming a macroscopic quantum system at almost zero temperature.

In a Bose-Einstein condensate, all atoms occupy the same quantum state. Theytherefore behave in exactly the same manner. By switching off the trap, the condensedatoms are easily seen by laser-imaging as they correspond to a peak of ultra-coldatoms on a background of uncondensed atoms (Fig. 2.3.10.3).

These condensates possessvery peculiar quantumproperties that are now beingactively investigated by morethan 50 groups in the world.They have interestingcoherence properties that, insome respects, are analogousto those of lasers. In a laser, avery large number of photonsoccupy the same mode of theelectromagnetic field, andthis property is at the originof the high brightness andlow divergence of laser beams.

Atom lasers have just beenproduced. Figure 2.3.10.1shows such a atom laser,developed by a group at the University of Munich, led by Prof. Hänsch. The very lowdivergence of the beam of atoms extracted from a rubidium condensate is clearlyvisible in that figure. As mentioned above, the main problem with these atom laserson Earth is that as soon as the atoms leave the trap they are accelerated by gravityand very quickly acquire a high speed. Obviously, the microgravity conditions of spaceshould be able to help in solving some of the fundamental questions that thesequantum systems raise. A second difficulty is the relatively low flux of atoms that acondensate can currently produce. Typically, a condensate of one million atoms isproduced in 30 seconds. Depositing these atoms on a 1 cm2 area will require about 30years! New methods for improving this situation are being actively investigated andone can expect, as for lasers, a considerable gain in output flux in the coming years.

2.3.10.4 Atomic Clocks

From the early days of atom manipulation using laser light, it was recognised that thevery low velocities of laser-cooled atoms would be of benefit in improving atomic

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Figure 2.3.10.3. The velocity distribution of a Bose-Einsteincondensate of rubidium atoms. The condensate forms anultra-cold peak (in blue) and the non-condensed atoms formthe green pedestal. At very low temperatures, only thecondensate exists (courtesy of Ecole Normale Supérieure,Paris)

Figure 2.3.10.4. The principle of an atomic clock. Anelectromagnetic radiation offrequency ν is tuned near theatomic frequency νo andtransfers the atom from theground-state energy E1 to theexcited state E2. The width ofthe resonance curve isinversely proportional to theduration ∆t that the atomsspend in the interaction zonewith the radiation. The methodproposed by N. Ramsey usestwo separated zones, in which case the width of theresonance is inverselyproportional to the time offlight T of the atoms betweenthe two zones. Slow atomsproduce a longer T


Figure 2.3.10.5. An atomic fountain. Caesium atoms arecooled to 1 µK and launched upwards at a velocity of 4 m/s.They twice cross a microwave cavity fed with a frequencyclose to the hyperfine transition frequency in caesium, onceon the way up, once on the way down. The time between thetwo interactions with the microwave field is about 0.5 s.Atoms that are excited by the field are detected below by alaser beam, in which they fluoresce

Atomic fountains have alreadyimproved the accuracy of atomictime by a factor of 10, and rapidprogress in stability and accuracy arecurrently expected. The bestfountains have a relative frequencyinstability of only 5 parts in 1016,which means that these clocks makean error of about 1 s every 50 millionyears! Today, 10 atomic fountains arein operation worldwide and about 20others are under construction.

2.3.10.5. Atomic Clocks inMicrogravity: PHARAO

In an atomic fountain, the downward pull of gravity obviously imposes a limit to theinteraction time, which is typically of the order of 1 s. Increasing this duration by afactor of 10 would require a clock height of 125 m. Such a size is not realistic, giventhe technical problems such as shielding of residual magnetic fields, and thermalstability. In microgravity, however, long interaction times can be achieved in a reducedvolume. It is sufficient to launch the atoms slowly in the clock device and to use thescheme for normal clocks shown in Figure 2.3.10.4, but with a launch velocity 1000times smaller. The principle of the PHARAO microgravity clock is summarised in Figure2.3.10.6. The resonance curves in a conventional clock, a cold-atom fountain and amicrogravity clock are compared in Figure 2.3.10.7. It clearly illustrates the gain inresolution that is made possible when laser cooling is used in conjunction with amicrogravity environment.

The relative frequency stability of the PHARAO clock onboard the International SpaceStation (ISS) is expected to be better than 10-13 for a 1 second measurement time,3x10-16 for 1 day, and 1x10-16 for 10 days. This accuracy is three orders of magnitudebeyond that of the clocks currently flying on GPS satellites.

Figure 2.3.10.6. The principle of the PHARAO cold-atom clock in microgravity. An opticalbench (top) provides light to a caesium tube for cooling and detecting the atoms, usingoptical fibres. Atoms are collected in ‘optical molasses’ in a first chamber (left), cooledbelow 1 µK, and launched into a second chamber. They enter a cavity in which theyexperience the two successive Ramsey interactions with a microwave field tuned near tothe 9 192 631 770 Hz caesium frequency. Atoms excited by this field are detected

downstream by fluorescence. Theresonance signal is used to lockthe oscillator’s central frequencyto the caesium transition. For alaunch velocity of 5 cm/s, theexpected resonance width is 0.1 Hz. This is ten times narrowerthan in Earth-based fountains

Figure 2.3.10.7. The advantage ofmeasuring cold atoms in microgravity.(a) A measured resonance signal in anEarth-based conventional thermal-beam caesium clock. The resonancewidth is 100 Hz.(b) A measured resonance signal withlaser-cooled atoms in a ‘fountain’ onEarth. The resonance width is 1 Hz.(c) The expected signal in the PHARAOspace clock, for an atom launchvelocity of 5 cm/s. The resonancewidth narrows to 0.1 Hz

N3/(

N3+N

4)

N3/(

N3+N

4)

∆v [Hz]

N3[u

.a.]

a time stability of 10 ps over one day, more than two orders of magnitude beyond thepresent GPS timing-signal accuracy.

The optical communication link hasbeen developed by the Côte d’AzurObservatory and CNES (F). CalledT2L2 (Time Transfer by Laser Link), itis based on laser pulses that aresynchronised to a ground clock andemitted, using a telescope, towardsthe satellite. The arrival times of thelaser pulses are dated onboard theISS and part of the light is retro-reflected towards the emittingground station by corner cubes onthe ACES platform. The retro-reflectedsignal is also dated in the groundclock’s time scale. This round-trip ofthe light pulses enables one to cancelthe fluctuations of the atmosphere inthe comparison between the groundand ISS time scales.

The microwave link transmits high-frequency signals between the Earthand the ISS. As in the case of T2L2,these signals are synchronised to theground and to space clocks,respectively, and allow one to comparethese clocks. Unlike an optical link,which cannot operate in cloudyconditions, the microwave link isweather-independent.

This equipment will fit on a nadir-oriented Express Pallet Adapter, withdimensions of 863x1168x1240 mm3.The total mass will not exceed 227 kgand the electrical power requirement is500 W. A mock-up of the ACES Pallet isshown in Figure 2.3.10.11.


A prototype of a cold-atom clock, developed by French laboratories with CNESsupport, was tested in the reduced gravity of aircraft parabolic flights in 1997 (Figs.2.3.10.8 and 9). This prototype is now a transportable cold-atom clock with anaccuracy of 1x10-15, which is presently the highest accuracy atomic clock. The satelliteversion of PHARAO, developed by CNES, completed its detailed design phase in 2000and will go forward to industrial development in early-2001.

2.3.10.6 The Atomic Clock Ensemblein Space: ACES

- The ACES mission

PHARAO was proposed to ESA in 1997,within the framework of a more generalmission called ‘ACES’. Selected by ESA tofly on the ISS as part of its earlyutilisation programme, ACES consists oftwo clocks, PHARAO and a hydrogenmaser (SHM, Neuchâtel Observatory,Switzerland). There are also optical andmicrowave communication links for timeand frequency transfer to ground-basedusers on the Earth (Fig. 2.3.10.10). Bothlinks are high-performance systems,designed to transfer the very highstability of the space clocks to theground without degradation bypropagation through the atmosphere.The projected performance of the links is

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Figure 2.3.10.8. ThePHARAO prototype undertest on the CNES Zero-GAirbus in 1997

Figure 2.3.10.9. ThePHARAO caesium tube(total length 1 m). Bottom: cooling zone.Middle: interaction zone.Top: detection zone andvacuum pump

Figure 2.3.10.10. The operating principle of ACES

Figure 2.3.10.11. Mock-up of the ACES Pallet

2.3.10.8 Future Prospects

PHARAO and ACES will probably constitute the first demonstration of the benefits ofspace for cold atomic gases and their application to ultra-stable atomic clocks.PHARAO’s performance could be improved still further by using a better interrogationoscillator, a better microgravity environment than that of the ISS, and by replacing thecaesium atoms with rubidium atoms, which display fewer collisional interactions.Frequency stability and accuracy in the 10-17 range can then be envisaged. Theassociated time- and frequency-transfer techniques will need to include several higherorder relativistic corrections in order to compare distant clocks adequately. Such ideasare already under development at NASA (PARCS, SUMO and RACE projects).

Of particular interest then would be a clock mission in the strong gravitationalpotential of the Sun, rather than that of the Earth (SORT). This mission could bringseveral orders of magnitude improvement in tests of general relativity, such as theShapiro delay. Third-generation navigation systems are likely to benefit from advancesmade in the time-transfer techniques validated with ACES. Totally new concepts forglobal positioning systems based on a reduced set of ultra-stable space clocks in orbit,associated with simple transponding satellites, could be studied.

More generally, on the ground clocks operating in the optical rather than in themicrowave domain are making rapid progress. The frequency of these clocks is four tofive orders of magnitude higher than that of microwave standards. With an equivalentline width, the quality factor of the resonance then exceeds that of caesium clocks bythe same factor. Using laser-cooled atoms or ions and ultra-stable laser sources, theseoptical clocks will likely open up the 10-17 – 10-18 stability range. Using the widefrequency comb generated by femtosecond lasers, it now becomes possible toconnect virtually all frequency standards together throughout the microwave to ultra-violet frequency domain. The simplicity of this femtosecond laser comb, which fits ona small optical bench, makes it conceivable to qualify it for space.

Clocks are not the only devices that can benefit from the space environment. Atominterferometers would also have increased sensitivity with increased interaction times.In these systems, matter waves rather than light waves interfere, bringing anenormous gain in potential sensitivity over light interferometers. After just a few yearsof existence, matter-wave gyroscopes on the ground have now surpassed their opticalcounterparts in terms of their ability to detect very feeble rotation signals. This opensup a whole new field for inertial sensors, accelerometers, and gradiometers, both onEarth and in space.

In January 2000, the HYPER project was submitted to ESA by a group drawn fromseveral European laboratories, in answer to the Agency’s Call for Flexi-mission (F2/F3)Proposals. HYPER is designed to measure yet another effect predicted by general


- Scientific Objectives of ACES

These are twofold:

– The first objective is to operate the PHARAO clock with the level of performancementioned above, i.e. a frequency stability of better than 3x10-16 for one day, andto study the effect of the reduced gravity on the clock’s stability and accuracy.

– The second objective is to use the very high stability of the PHARAO-SHM combinedtime scale, onboard the ISS, to perform time comparisons between ground clocks,to a 30 picosecond level of precision. This represents an improvement over the bestcurrent GPS comparisons by a factor of 100. Frequency comparisons between theseclocks will be performed with a relative accuracy of 10-16, whereas at presentfrequency comparisons between distant clocks have not been performed below 10-15.

– The third objective is to perform several fundamental-physics tests with increasedprecision. The gravitational red-shift will be measured with a 3x10-6 accuracy, a 25-fold improvement over the NASA 1976 Gravity Probe-A mission. Better tests of theisotropy of the speed of light and a new search for a possible drift in one of thefundamental physical constants, the fine-structure constant α, will also be performed.

Figure 2.3.10.12 illustrates the progress made in the last forty years with atomicclocks in the microwave and optical domains. In 2005, ACES is likely to be near to thecrossing point of microwave and optical clocks, providing a very interesting spaceoption for comparing these ultra-stable clocks on the ground.

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Figure 2.3.10.12. Evolution in the accuracy of atomic time, comparing microwave andoptical clocks

relativity, namely the Lense-Thirring effect, and also to measure the fine-structureconstant with at least one order of magnitude gain in precision. HYPER would also bethe first satellite to be monitored and controlled using matter-wave inertial sensors,rather than classical accelerometers and gyroscopes.

The technology for producing Bose-Einstein condensates and atom lasers is alsoprogressing rapidly. Space would offer the possibility to produce coherent atomicwaves in the picokelvin temperature range. In addition to the interesting fundamentalmany-body physics that this quantum matter would offer on a truly macroscopicscale in space, atom lasers would constitute ideal sources for atom interferometerswith long interaction times.

Clearly, cold atoms open up several new and fascinating prospects for spaceapplications!

Acknowledgements

The author wishes to thank many European and US colleagues for fruitful discussionson the above topics. The support received from ESA, CNES, CNRS, Region Ile de France,Bureau de Metrologie, and the Paris Observatory is also gratefully acknowledged.

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CHAPTER 3 FROM BASIC RESEARCH TO

COMMERCIAL APPLICATIONS

3.1 The Scope and Impact of the Information and Technology Transfer

G. Seibert

Research and development programmes stimulate the production capacity of theeconomy through the development and introduction of new technology. This can beparticularly the case for space-related programmes, which require technical solutionsfor an extreme environment. New technology can make existing production methodsmore efficient and it can create new products, instruments and services. These notonly stimulate new markets, industries and opportunities, but can also improve theway people do things and the overall quality of life.

These benefits and their impact on the economy are not immediate; it often takesmany years for a new idea to be transformed into a marketable product or service.Economic success will also generally require large-scale manufacturing capacity,marketing effort, advertising, and product support.

Within the framework of the European space effort, some 4 billion Euros per year havebeen pumped into the economy, resulting in the creation of jobs and the stimulationof income throughout Europe. Of that amount, the ESA programmes have contributedsome 2.6 billion Euros annually over the past decade.

The basic role of ESA is to carry out approved space programmes on a Europe-widebasis. An important part of that task involves the development of leading-edgetechnology to support those programmes. The developments may be in areas such aslaunchers and space systems, in communications, or in support of the diversescientific and applications payloads.

Inevitably, some of these advanced technology developments find their way intoapplications other than just the space application originally intended. The result may


The large number of spin-off developments from the microgravity space life sciences,which have found medical applications on Earth, is especially rewarding. It takesabout 5 years to perform the necessary clinical tests and to obtain the related safetycertificate for medical application. That points to an early and rapid application of theoriginal space technology.

It was observed that the applications were often developed through the combinedinitiative of the Principal Investigators and those companies that were involved in theoriginal microgravity hardware development. The main reason for the great success ofthis microgravity spin-off process is probably the fact that research activities inmicrogravity life- and physical sciences are closely linked to terrestrial research in thematerials industry and in medicine. The space programme therefore acts as acatalyser for the development of innovative instruments and technologies.

In the following Sections, some of the most notable spin-off developments that wereidentified in this study are reviewed and their commercial relevance indicated.


simply be a use in some other highly specialised system of no great commercialconsequence. On the other hand, it may also be adapted to find widespread andvaluable commercial application. Consequently, the ESA programmes provide not onlya direct return in the shape of successful space endeavours and a stimulation ofEurope’s economy and its space technology, but they also add indirect benefits. Oneof these is the process of ‘spinning-off’ advances in technology to create new,commercially valuable products.

The total extent to which this process operates is difficult to quantify. Knowledge is likea freely flowing fluid that can take many routes, so that the eventual destinations ofthe transferred knowledge can be difficult to trace. Nonetheless, ESA has initiatedstudies to try to get a measure of this so-called ‘spin-off’ effect. These Spin-Off andTechnology Transfer Studies are intended to provide concrete examples that illustrateadvances made as a result of space-technology research and development. They coverareas such as medical instrumentation and services, new and better materials andprocessing techniques.

In addition to that action to look back at what has happened and how various spin-offs have occurred, ESA and several European national space agencies have also takenthe initiative to actively encourage and to promote this technology-transfer processfrom space programmes. A Space Link Group composed of transfer agents from ESAMember States has been formed to support these activities, and the major spaceprogrammes are now routinely examined for possible technology-transfer candidates.

The cost of the ESA Microgravity Programme amounts to less than 3% of the total ESAbudget. Consequently, it had not been in the focus of this general ESA initiative toidentify and define technology-transfer candidates. In fact, it was not until late 1999that the Microgravity Programme was included in these activities and the task begunof identifying the spin-offs from the microgravity research and its associatedexperimental facility developments. In this task, and that of trying to estimate thepotential markets, ESA was assisted by industry (Novespace/Beta).

The outcome of this review revealed an extraordinary success. Fourteen technicalitems, derived from microgravity life-science and materials/fluid-science activities,were either already on the commercial market, or about to produce large quantities ofterrestrial equipment in newly built factories. Several space companies have recentlycreated spin-off companies. For the year 2001, the commercial value of these spin-offsfrom the microgravity programme is estimated to be in the order of 50 – 60 millionEuros. In 2002, it is expected to be in the range 90 – 100 million Euros, with furtherincreases for the following years. The annual revenue associated with these spin-offdevelopments from the microgravity programme will actually exceed the annualpublic funding spent on the ESA microgravity space activities.

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- Spin-Off ‘Selftonometer’

The next step was the application of thistechnology to clinical medicine. An evenlighter, smaller, more precise one-handinstrument was developed from thespace model. Using the same IR-detectorand the same technology proven inspace flight, an automatic Selftonometerfor use by glaucoma patients wasdeveloped in co-operation with ElektronikPräzisionsbau Saalfeld (EPSa) at Jena-Saalfeld (D). Following calibration,extended clinical tests and instrumentcertification (CEN) in 1999, this instrument could be made available to glaucomapatients.

- Economic Aspects

Originally part of the East-German Zeiss-Kombinat in Jena, today EPSa is a privatecompany with 140 staff, working mainly in the fields of small medical equipment andtraffic telemetry using GPS. The research and space-hardware developments weresupported by the German Space Agency, but EPSa has invested about 1 million DM inthe development and commercialisation of the Selftonometer, plus 0.5 million DM inthe large-scale production tools. The commercial activities started in 1999, with thesale of 500 Selftonometers at a unit price of 2000 DM. In 2000, 1000 units were sold,and for 2001 sales of 5000 units are envisaged. A contract with the German associationof pharmacists has been concluded. They have taken over the task of instructingpatients in how to operate the device. Also, the health-insurance companies haveagreed to take over a major part of the procurement costs for the patients. The medicalinstrument company SMP markets the Selftonometer worldwide.

In 1999, marketing also started in Italy, Austria and Switzerland. It also started in2000 in the USA, where a very large market exists. In Germany there are 1.5 millionglaucoma patients, about 500 000 of whom are expected to buy a Selftonometerdevice. In addition, another 500 000 units are planned to be sold in other Europeancountries. The eventual largest market is expected to be in the USA, with a likelyrequirement for several million Selftonometers.

There is also a version that allows eye-doctors to treat babies and handicapped people(costing 3000 DM). The Selftonometer has been patented in all major countries of theworld. A follow-up development, compatible with telemedicine, is being tested at theUniversity of Erlangen (D).


3.2 The Commercial Spin-Off from European Microgravity Research

G. Seibert

3.2.1 Glaucoma Diagnosis: the ‘Selftonometer’

Glaucoma is a widespread eye disease. It afflicts about 70 million people in theindustrialised world and has led to blindness in about 10% of patients. It is caused byelevated pressure within the eye. If this intra-ocular pressure exceeds the vascularpressure within the arteries of the retina, the blood flow is suppressed. Consequently,the blood supply to the nerves may then become inadequate and the nerves of theretina die, producing blindness. If, however, the glaucoma is regularly checkedthrough pressure measurements (six times per day) to detect pressure peaks,medication can be used at the appropriate time in order to lower and regulate the eyepressure. This can substantially reduce the risk of blindness occurring.

- Space-Related and Technical Aspects

It was believed that the fluid shift observed in astronauts when they enter themicrogravity environment of space would have a strong effect on their intra-ocularpressure. The quantitative measurement of this pressure and its time dependence wasthe subject of various space experiments by Prof. Draeger of the University ofHamburg.

On the German D-1 Spacelab mission in 1985, the eye pressure of an astronaut wasmeasured. This could only take place one hour after launch (i.e. too late to measurethe peak) and it needed an additional astronaut to act as the operator. The drasticallyincreased pressure that occurs during the launch itself could not be measured.Therefore the development of an automatic selftonometer device was needed and onewas subsequently developed. This new device enabled an astronaut to measure hisown eye pressure anywhere and at any time, even during launch and landing.

The main objective of the new development was to obtain a simple, one-man-operatedinstrument for astronauts. Different sensors were tested. Finally an optical infrared-surface detector was chosen, allowing for precise definition of the applanated cornealsurface whilst performing tonometry. This light and precise instrument allowed self-tonometry to be performed under microgravity conditions for the first time. It wasused during the Mir-92 mission and on the German D-2 Spacelab mission in 1993. Arapid increase in intra-ocular pressure, to 100% above the normal value, wasmeasured. Fortunately, there was also an early (within a few hours) re-adaption tonormal levels. After landing, a marked drop in intra-ocular pressure was recorded.

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Figure 3.2.1. The ‘Selftonometer’, aninstrument for routine monitoring of intra-ocular pressure in glaucoma patients,derived from a self-operated instrumentused by astronauts (courtesy of EPSa)

Space) ESA developed a Bone Densitometer device, which was based on a quantitativeultrasound technique. This technique was chosen to avoid the use of ionising radiationin a manned spacecraft, as would occur with the normal Dual X-Ray Absorptiometrytechnique.

The ultrasound Bone Densitometer determined the speed of sound and the broadbandultrasound attenuation in the bone at the heel (calcaneus), and later at the tibia. Fromthese two parameters, accurate information on bone mineral density and on bonestructure can be derived.

The small French company Medilink, a subsidiary of Diagnostic Medical Systems, hasdeveloped the terrestrial spin-off of this Bone Densitometer, called ‘Osteospace’, undera licensing agreement with GIP-Ultrasons and Matra.

In 2000, around 100 Osteospace units were sold to clinics and practitioners, at a priceof 18 000 Euros. Over the next two years, DMS foresees sales of this unit doubling. Animproved version will be a portable unit, with new and improved probes. The worldmarket for bone densitometers is currently worth about 600 million Euros/year. InEurope, some 5000 units were needed in 2000 by radiologists, rheumatologists andorthopaedists.

3.2.3 Video Oculograph

Within the framework of the visual-vestibular research performed in microgravity onthe German and ESA missions to Mir (1992–96), the German national spaceprogramme has supported (since 1987) the development of a Video Oculograph (VOG)by Prof. Scherer, of the FU Berlin. That original instrument was later extended to aBinocular Video Oculograph (BIVOG), and used as a research instrument by Mirastronauts from Germany, ESA and Russia.

Making use of the technology and operational knowhow developed from the spacemissions, SensoMotoric Instruments (SMI) was founded in 1991 to concentrate on thedevelopment of VOG systems for terrestrial applications. The performance of thisinstrument was also improved and its innovative features extended. This resulted inminimising the inertial load on the head by the use of lightweight components for theHead Unit, and an extension of the field of view.

The applications for these instruments (2D-VOG and 3D-VOG) are in the medicaldiagnostic area, such as ophthalmology, neurology, physical therapy and in therelated clinical and psychology research, such as brain research, human factors andmarketing. So far, more than 500 of the eye-movement systems have been sold andinstalled in Europe, America and Asia, where the company has set up subsidiaries ororganised a distribution network with competent partners.


3.2.2 Osteoporosis Diagnosis: the ‘Osteospace’

The absence of weight in the microgravity of space gives rise to changes in thosetissues that normally support the body and propel it. The result of this unloading is aprogressive reduction in bone and muscle mass. (see Sections 2.1.4/5). Theseprocesses are known from long-duration space missions, such as Skylab (lasting up to84 days) and Mir (lasting up to one year).

Bone has two basic components, living and non-living. The living element is made upof osteoblast cells,which help to form new bone, and osteocast cells that resorb oldbone. The non-living component is a matrix of collagen multiple fibres, combined withcrystalline salts of calcium and phosphates. The former provide the bone with greattensile strength, while the latter give high compressional strength.

The rates of bone deposition and absorption are essentially equal in a normallyfunctioning body on Earth, so that the total bone mass remains constant. Thisequilibrium is influenced by a number of factors, such as nutrition, physical exercise,exposure to sunlight (vitamin D), and hormonal secretions from numerous bodyglands. When the osteoblastic activity in bone is less than normal, the disease knownas ‘osteoporosis’ develops (i.e. porous bone), which afflicts many women after themenopause and also the elderly. The bone loss can amount to one third of the originalbone mass in women and half of that in men, the latter having about 30% more bonemass to start with. Osteoporosis makes bone brittle and more susceptible to fractures.The low bone mass and structural deterioration of bone tissue lead to an increasedsusceptibility to fractures of the hip, spine and wrist. A similar effect to osteoporosisdevelops in astronauts during spaceflight, but in an accelerated form. It is primarilythe result of the disuse of the weight-bearing bones in the microgravity environment.

In order to study the rate of bone mass loss in astronauts and to determine whethercountermeasures (physical exercise), medication and nutrition are sufficientlyeffective, a number of European scientists were selected to perform research duringESA’s two Mir-based missions in 1994 (duration 30 days) and 1995 (duration 179days). In support of these bonestudies in space, via contractswith industry (Matra Marconi

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Figure 3.2.2. The Osteospace, a bonedensitometer derived from a space

instrument uses ultrasound todetermine bone density and structure,rather than the X-rays of conventional

systems, thereby avoiding radiationexposure for the patient (courtesy of

DMS/Medilink)

particular method of sterilisation was preferred due to its lower technical resourcerequirements and better safety features, when compared to conventional disinfectionfacilities such as autoclaves.

Bradford have derived a commercial version of this Biolab disinfection system, knownas the ‘Sterilite’. This ozoniser box is available in two versions: one is a portable unit,whilst the other is intended for permanent installation for all types of sterilisation anddisinfection work. It can replace the traditional and cumbersome steam autoclaves,which work at high pressures and at 120ºC. The chemically aggressive ozone thatdoes the disinfection is generated by the ionisation of oxygen in the air, using a thinwire at a high electrical potential (7 – 8 kV). After the disinfection treatment, the ozoneis easily dealt with because it decays naturally to normal oxygen with a half-life of 5minutes.

There is a large potential market for this system, ranging from hospitals and clinicsthrough to biochemical laboratories and dentists’ facilities. Bradford’s market analysisand production capability (large-scale production planned to start in autumn 2000)projected 1000 units for the year 2000, equivalent to 2.3 million Euros. Afterintroduction of the ozoniser to the market, it is estimated that the total world demandfor Sterilite could be as high as 100 000 units. Bradford anticipates that sales willincrease further in 2001 and 2002, to 6 and 10 million Euros, respectively.

3.2.5 Triple-Containment Glovebox

Bradford Engineering developed various versions of a triple-containment biologicalglovebox for ESA in the early 1990s, which were intended for the USML-1 and USML-2Spacelab missions. It also extended thisdesign, to develop the larger glove boxesthat were sold to NASA and to theJapanese space authorities. These wereflown on several Spacelab and Spacehabmissions. In modified versions, thisglovebox has found customersworldwide for various spaceprogrammes.

A commercial development of these verysafe, triple-containment spacegloveboxes was made by this company,aimed at the much wider non-spacemarket. These units provide for thecontrol of gas composition and pressure,temperature and humidity. They allow


The 3D-VOG instrument, which alsomeasures the torsional movement of theeye, is so far only used in a small number ofinternational research institutes, eye clinics and by the German Air Force. Recently,SensoMotoric Instruments launched a new product (STRABS) based on thistechnology, which enables on-line binocular measurements and squint angleevaluation in three dimensions (horizontal, vertical and torsional), needed forstrabismus (squint) analysis. Both instruments are based on a face mask, whichincludes two high-resolution infrared cameras mounted on the sides of the mask, towhich the eye images are reflected using visible-light translucent IR mirrors in front ofthe eyes. The video image of the eye is digitally processed and the squint anglecalculated. A large variety of visual stimuli can be applied by displays in front of thepatient, using a video projector.

SensoMotoric Instruments has specialised in the development and system integrationof video and sensor technology associated with digital image and signal processing foreye-tracking systems. Whereas the 2D-VOG has had great success in clinics forvestibular examination of patients (nystagmography analysis), the 3D-VOG is mainlyused for research purposes. Other products include ‘EyeLink’, which is the leadingresearch product for eye-movement analysis, and ‘iView’, used for human-factoranalysis.

The German national microgravity research programme supported the VOG spaceproject in the period 1987–1996. A follow-on development of an Eye Tracking Device,based on VOG and BIVOG, for research on the Space Station, is presently beingsupported by DLR at FU Berlin. The world market in this field of video-oculography andeye-movement measurement products is US$15 million, of which SMI hasapproximately 30 to 40%. SensoMotoric Instruments presently has a staff of morethan 30 people. It is the technology leader in eye-tracking solutions for research,medical applications, human-factor analysis, as well as industrial applications.

3.2.4 Ozone Disinfection: the ‘Sterilite’

Bradford Engineering (NL) have developed a safe disinfection system that is basedupon flush cleaning with ozone gas. It was originally designed for use in the Biolab, amulti-user facility for biological research on the International Space Station. This

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Figure 3.2.4. The Bradford Triple-Containment Glovebox. Originally used inspace for ESA microgravity research, theseunits have been bought by NASA and theJapanese Space Agency. A design forterrestrial use has found application inmedical areas and for the handling of toxicmaterials (courtesy of Bradford BV)

Figure 3.2.3. The Video Oculograph, aninstrument derived from research on the humanvestibular system in space. The measurement ofeye orientation and movement finds application

in clinical practice in ophthalmology, inneurology and in psychology research (courtesy

of SensoMotoric Instruments)

support of these lung experiments, ESA charged the Danish company Innovision withthe development of a Respiratory Monitoring System (RMS).

Innovision’s space work began in 1986 with the development of an early respiratorymonitor that used a bulky mass-spectrometer as the gas analyser. It was flown as a majorelement of the ESA Anthrorack on the German D-2 Spacelab mission in 1993. Theprincipal purpose of the monitor is to analyse the composition of respired gas mixtures.

A second generation of this monitor was subsequently developed. For the analysis ofthe respired air, it used the smaller Photo Acoustic Spectrometer (PAS) gas analyser,developed and patented by Bruel and Kjaer (DK). This instrument was flown with all itsperipheral equipment on ESA’s Euromir ’95 mission.

The third generation of this respiratory gas monitor, with an improved performanceand reduced resource requirements, is being developed for the STS-107 Spacehabmission in 2002. In addition, Innovision is currently developing for ESA a Photo-Acoustic Module for the pulmonary function instrument of the Human ResearchFacility. This will be installed in the International Space Station.

- A Commercial Respired Gas Analyser

Stemming directly from the respired gas analyser developed under an ESA contract,Innovision has derived a commercial instrument, the AMIS-2000, which is intended foruse in pneumonology, cardiology, intensive care and sports medicine. A secondinstrument, the AMIS-2001, uses the photo-acoustic gas analysis method and hasbeen clinically evaluated in Denmark, Germany, the United Kingdom, Sweden andItaly. The market for such gas analysers for clinical applications is potentially verylarge. Heart/lung failure is the most important health problem of the industrialisedworld, and a non-invasive technique to determine the condition of both the cardiacsystem and the lungs is highly desirable.

With this technique, measurements are made of the contents and flow of a person’srespired gas. From these it is possible to determine the volume of blood pumped perminute (the cardiac output), lung diffusion capacity, lung volume, and the rates ofoxygen uptake and of carbon-dioxide excretion. This provides much of the basicinformation needed to guide medical diagnosis and the appropriate treatment.

Innovision has therefore put a major effort into developing third-generation gasanalysers for non-invasive measurements of cardiac output, etc. The new analyserswill be dramatically improved in terms of technical capabilities compared with theAMIS-2000: 8 kg instead of the 100 kg of the AMIS-2000, 30 W instead of 800 W,signal-to-noise ratio of 2000 instead of 400, and a two times better response time thanthe AMIS-2000. The price is also very much lower, at 15 000 instead of 70 000 Euros.


for the provision of a video system and internal microscopes and for the handling oftoxic substances. The glovebox allows the partial pressure and the mixture of gases tobe set and accurately controlled. Since body cells in-vivo see a 4 to 5% oxygen partialpressure, rather than the 21% as in air, this facility has become a very desirable toolfor cancer research and for artificial- insemination studies. (in the USA there are 4million artificial inseminations per year). Cancer-research institutes are alreadyworking with a terrestrial version of this glovebox.

The market for the triple-containment glovebox is potentially large and alreadyincreasing. After the first 8 units were produced and sold for 1.6 million Euros in 2000, sales will increase to 6 million Euros in 2001, according to Bradford’s businessplan. In order to manufacture the Ozonisers and Gloveboxes in large quantities,Bradford BV created a sister company, Bradford Medical, in 1999.

3.2.6 Heat Exchanger

In another commercial application of its space work, Bradford Engineering hasdeveloped a terrestrial version of its space component the ‘Flat Swinging Heat Pipe’,for application by the aviation industry. This unit is a direct derivation of thecooperative development by Bradford and the Dutch institute NLR of a two-phasetemperature-control system. Its technical performance was first demonstrated in anESA General Supporting Technology Programme experiment and it was later used inspace for a combined ESA/UK project.

The commercial derivative of this component has gained acceptance by the militaryaviation authorities. From 2002 onwards, it will be used in large quantities for a newmilitary aircraft, i.e. about 20 units per fighter plane. Some 3000 such planes will beproduced by Boeing/Raytheon, as a successor to the Starfighter.

However, Bradford is also active in finding customers in the non-military sector, inwhich it expects significant sales already in 2000/2001. The initial annual sales targetis 2.5 million Euros (unit price 400 Euros). An investment of 1.2 million Euros isplanned by Bradford, which includes the setting up of a production line. The low andhigh business scenarios vary between 4000 and 20 000 units per year.

3.2.7 Respired Gas Analyser

Prof. D. Linnarsson of the Karolinska Institutet in Stockholm, and Prof. M. Paiva of theFree University of Brussels, in co-operation with cardiopulmonary scientists from theUSA and Australia, wanted to study whether the upper and lower parts of the lunghave different air- and blood-flow patterns when in space, compared to those when onthe Earth. In other words, are these patterns induced by gravity on Earth and thereforeabsent in microgravity, or are these patterns a natural property of the lungs? In

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- Spin-Off ‘Dry Toilet’

The company 3IS identified a significant terrestrial application for this space waste-management device in various transportation vehicles such as buses. It is very suitablefor use in campers/caravans and also on airplanes, both large and small, where wateris scarce and expensive to transport. Boats in harbour are another potential user, sincethe fouling of harbour waters is a serious problem with present water toilets.

In such applications, the dry toilet has had to meet government regulations forbiddingthe open discharge of pollutants. The dry toilet meets both the technical requirements(minimum mass/volume), by avoiding the need for large amounts of water, and theregulatory requirements of` disposal, by using plastic-bag containment, perfectly. It isto be preferred also from the hygiene point of view.

3IS has patented the dry toilet in 12 countries, including the USA and Canada. Underlicence from 3IS, the company Actia has started industrial manufacture of the DryToilet for camper vans and buses. It has installed test units in buses in France, Spainand Mexico.

Actia has invested some 300 000 Euros in the installation of an industrial productionline and has concluded delivery contracts with the car industry (Renault) and caravanproducers for the installation of the dry toilet. The unit cost for buses is 2000 Euros,whereas the unit cost for a simpler, lower capacity system for a camper van costs just200 Euros.

The overall European market for new camper vans is about 20 000/year. It is thereforeexpected that, including the boat market, some 2000 units will be sold in 2001. Thatshould increase strongly by 2002. The present market for buses is 200 units/year andis expected to increase to 300 by 2002.

In addition, 3IS is presently developing a modified dry-toilet version for hospitals,called ‘Hospack’. A further application is its use by customs authorities for the collectionof faeces from people suspected of having ingested tiny plastic bags filled with drugs.

The market for dry toilets is therefore expected to become a multi-million Eurobusiness in the near future.

3.2.9 Three-Dimensional Eye Tracker

In the early 1990s, the German national space programme supported Dr. Clarke andProf. Scherer in the development of their Video-Oculography (VOG) and BinocularVideo-Oculography (BiVOG) measurement technology for vestibular research. With thehelp of industrial partners, these image-based eye and head-movement measurement


In addition, the maintenance requirementsand complexity of operation of the newinstruments are greatly reduced. Theportable version of this device can be placedin the patient’s home to monitorcardiovascular and respiratory parametersroutinely. This is valuable in that it avoidshospitalising patients, for example thosewith pacemakers, dialysis, and critical careneeds.

The market for this third-generationcommercial instrument is probably verylarge. The main clinical application focuseson the measurement of cardiac output(pumping capacity of the heart) by a non-invasive method. It is very likely that thisnew method will replace the presentlyapplied invasive methods, which are costly,inconvenient for the patient, and involverisks. The new technology is expected to contribute towards reducing the mortalityrate from cardiovascular diseases, one of the most common causes of death in theindustrialised world.

- Spin-Off Ergonometer

The Bicycle Ergonometer developed by Innovision for ESA was intended to be used asstimulus equipment for cardiopulmonary research. However, Innovision hassubsequently sold 15 such units (100 000 Euros each) to NASA, for use by Shuttleastronauts for exercising whilst in space. It has also found use in several researchcentres and in the anaesthesia and intensive-care departments of hospitals/clinics.

3.2.8 Waste-Management Devices

In the early 1990s, CNES carried out a research programme in space using Rhesusmonkeys. Within the framework of this programme, it was necessary to develop asystem to collect the monkeys’ waste under microgravity conditions. The technicalrequirements for the development called for a simple system, having a low mass andvolume.

The small French company 3IS and Soterem took up this challenge and designed anddeveloped a dry toilet system that collected and packaged the urine and faeces insealed plastic bags.

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Figure 3.2.5. The Innovision RespiredGas Analyser. Derived from a spaceinstrument for ESA, it provides a non-invasive method of determining cardiacoutput and lung characteristics andfunctions (courtesy of Innovision)

3.2.10 Ultrasonic Components

In 1979, Prof. L. Pourcelot and Dr. Patat of the medical faculty of the University of Toursstarted to develop, in co-operation with Matra Espace, an ultrasound sensor toperform heart echography during spaceflight. This work was carried out within theframework of the CNES Premier Vol Habité programme. The first French astronaut, J.L. Chretien, used this echograph in 1982 in orbit. A follow-on development of thisdevice, the ‘As de Coeur Echograph’, was used in 1986/87 by the second Frenchastronaut P. Baudry, on Mir and on Shuttle mission STS-51.

Matra itself did not want to enter the terrestrial medical-equipment market. However,two spin-off companies were created: Vermon (1984, Tours) by the Faculté deMédecine de Tours, and Imasonic (1989, Besancon), by Vermon engineers involved inthe space projects. The intention was to manufacture and commercialise ultrasonicDoppler probes and transducers for the medical-equipment industry.

In addition, a Groupement d’Interet Public called GIP-Ultrasons was created in 1990 atthe University of Tours by several of the university’s research institutes, CNES, Matraand a number of academic, governmental and private institutions. This GIP had theobjective of compiling, advancing and transferring ultrasonic technology, includinghigh-resolution ultrasound imagery. Matra transferred its ultrasound know-how fromthe ‘As de Coeur’ space project to GIP-Ultrasons. This group participated in severalspace ultrasound projects in the 1990s, e.g. in the design and development of the ESABone Densitometer and in ESA technology studies in this field. In addition, it started toderive the spin-off ‘Osteospace’ (see Section 3.2.2) and UBIS 3000, a device thatenabled the mapping of parts of the bone at different times.

In 1997, experienced GIP-Ultrasons engineers created the small company ‘UltrasonsTechnologie’, which produces and markets ultrasonic equipment for diagnosticimaging and components. The ultrasound Doppler transducers and probes for theseare produced by the company Vermon.

The company Imasonic is specialised in the techniques that are used for non-invasivemedical diagnostics and therapy and in non-destructive testing and control ofmaterials and parts in industry. It provides piezo-components made from compositematerials for large frequency ranges, wide temperature ranges and acoustic powerdevices.

Together, these three companies, Vermon, Imasonic and Ultrasons Technologie,employ more than 100 people. In 1999 they had an annual turnover of 10.5 millionEuros, at least 50% of which was directly derived from the space life-sciences-facilitydevelopments.


systems were implemented for deployment on the German and ESA missions to Mir.Based upon this space technology, the company SMI (as discussed in Section 3.2.3)developed a first commercial spin-off. This was based upon standard video technology,which permitted off-line analysis of eye-movement recordings. Now Chronos Vision,which is a small enterprise founded by Dr. Clarke and Dr. Baartz of the FU Berlin, hasdeveloped the next-generation VOG, the 3D Eye Tracker. This provides for fully digitalmeasurement of eye movement. This new system is based upon state-of-the-art,programmable, CMOS image sensors and dedicated digital processing devices.

The 3D Eye Tracker is designed as a portable instrument, being intended in the firstinstance as an integral part of the Human Research Facility on the ISS. However, it isalso being developed as a commercial instrument for neurological andophthalmological examinations. The Eye Tracker provides on-line and off-linebinocular measurement of horizontal, vertical, and torsional eye position, based upondigital recordings of image sequences. Important new features include a selectablesampling rate of up to 400/second, reconfigurable processor units to allow softwareupgrades, and an ergonomically designed head unit.

The main market areas for the ‘Chronos 3D Eye Tracker’ include:– medical research and diagnosis in neurology and ophthalmology– monitoring of eye movements after corrective retinal surgery– monitoring of eye position during laser refractive surgery– neuro-psychology research and rehabilitation– multimedia applications, such as eye-guided interactions in virtual environments– ergonomic studies.

Preliminary clinical tests are now being performed in neurology clinics and vestibularresearch institutes in the USA, Canada, Germany, France, and Switzerland. The 3D EyeTracker will be marketed worldwide by the experienced Dutch company SkalarMedical BV. The initial market for these units is estimated to be in the order of 60 – 80per year. The unit price is about 35 000 Euros.

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Figure 3.2.6. The ChronosVision 3D Eye Tracker headunit. Originally developed forthe German Space Agency andflown on German and ESA Mirmissions, it offers binoculareye-movement recording,using integrated, intelligentcameras. The design gives afree field-of-view and the face-mask provides a comfortable fit that eliminates slippage. It is used for ophthalmologicaland neurological examinations, in corrective eye surgery, and in eye-guided interactions invirtual environments (courtesy of Chronos Vision)

accuracy that is about 1/10 000 of the sizeof the object. Calibration of the system canbe performed in the field and takes only afew minutes.

- Economic Aspects

There is a rapidly growing demand for accurate and mobile three-dimensionalmeasurements in many industrial areas, such as the automotive, aircraft, ship andtool industries. Efficient and very precise production monitoring, quality control andassurance is essential in modern industry.

The Pro-Cam3 system has advantages over competitive techniques such as StationaryCo-ordinate Measurement Machines, Mobile Measurement Arms and StereoVideogrammetry with regard to handling, mobility, setup time and portability. Theaccuracy is slightly lower than with these alternative techniques, but it is generallysufficient. In addition, the cost is lower.

The expected annual market volume is 50 Pro-Cam3 systems from the year 2001onwards, following introduction in 2000. The unit cost is 65 000 Euros. It is expectedthat the market for this unit will increase annually by about 30%.

Among the initial users are Daimler Chrysler and BMW in the car industry and AirbusIndustrie. The Pro-Cam system has been patented in Germany and patent applicationshave been made by AICON in other European countries and in the USA.

3.2.12 Crash Tester for the Car Industry and Railway Electrical Monitor

Kayser Threde GmbH, of Munich, has been involved in the Texus Sounding-RocketProgramme since it started in 1976 in Germany. The Texus Programme was initiallydedicated to short-duration microgravity experiments in materials science, fluidphysics and later also biological experiments.

These experiments were performed with a set of experiment modules, such asfurnaces, process chambers, biological incubators, etc., equipped with an integratedelectrical supply, command and data-management system, telemetry, and g-level


3.2.11 Mobile Photogrammetric Measurement System

Within the framework of ESA’s fluid-science activities in microgravity, there was a needto measure the motion and shape of transparent liquid bodies, e.g. the liquid columnsinvestigated with the Fluid-Physics Module and also with the Advanced Fluid-PhysicsModule flown on the German D-2 Spacelab mission in 1993.

The traditional measurement technique used to determine both the geometrical shapeand the volume was the so-called ‘light sheet method’, which provides successivemeasurements of the cross-sections. This technique is limited to steady-statephenomena or to a single cross-section.

In order to remove these limitations and the risk of microgravity disturbances by amechanical scanning system, ESA placed a technology study to develop a techniqueto observe the dynamic behaviour of arbitrarily shaped fluid bodies in a fluid matrix.This was to be based upon the use of a three-dimensional photogrammetric method.

In the period 1993 to 1996, the small company AICON in Braunschweig (D), translatedan idea of Mr J. Becker (ESTEC) into hardware and software that could measure thechanging shapes of liquid columns, droplets and bubbles. AICON’s expertise led to thecreation of a 3D Photogrammetric Measurement Head for the measurement ofposition co-ordinates throughout the whole object space, i.e. throughout the wholeexperiment volume (typically 100x100x100 mm3) with a spatial resolution of 15 microns.

This non-invasive optical diagnostic tool can be applied, for example, to the Fluid-Science Laboratory for the Space Station, in order to study dynamic phenomena fromone viewing direction, whilst leaving the second orientation open to other diagnostictools. The system is also able to perform the three-dimensional reconstruction ofobjects. The front end, towards the object to be measured, consists of a ‘camerabundle’ of three CCD cameras that provide different views of the object. Using thesethree different views, the position co-ordinates can be calculated on the basis of asystem calibration. This calibration includes the orientation of the cameras and the‘multi-media optical path’ (e.g. air–windows–media–bubble).

- Spin-Off ‘Pro-Cam’

AICON has used its experience from space-related work and from earlierphotogrammetric work to develop an industrial 3D measurement system, thePro-Cam3. The industrial version of this mobile 3D-probe has been accommodated ina handy solid housing connected via a cable to a portable PC, which directly displaysthe co-ordinates. Exchangeable probe tips (touch sensors) have been provided.

The measured shapes and volumes range from some centimetres to 10 metres, with an

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Figure 3.2.7. The AICON Pro-Cam3. Originallydeveloped to measure the 3D motion and shape

of transparent liquids in ESA fluid-physics facilities,this commercial derivative finds ready application

in many industries where simple, yet accurate,three-dimensional measurements and image

reconstitutions are required (courtesy of AICON)

ESA’s plan was to have a measurement device to determine the well-known shift ofabout 2 litres of body fluid that occurs in astronauts when they enter the microgravityenvironment. This NTE contract also covered the performance of two MUFI calibrationand application campaigns, which were carried out with the involvement of severalmedical teams with expertise in body-fluid shift mechanisms and in different methodsof determining segmental and global total and extra-cellular water volumes.

The MUFI measurement technique uses the fact that the electrical impedance ofbiological tissue is a function of frequency. The impedance has a real and an imaginary(typically negative) part, with the latter indicating capacitative effects originating fromcellular membranes. When the frequency of the current injected into the ‘circuit’ of thebiological tissue is low (below 20 kHz), the capacitor C (of the membranes) has a highimpedance and current flows only through the extra-cellular medium (Re). If thefrequency is high, (i.e. over 100 kHz), then the capacitor C becomes almost a short-circuit and the electrical current flows not only through Re, but also in parallel throughRi (the resistance of the intracellular medium) via the capacitor C. This means, in simple terms, that at frequency zero the extra-cellular fluid volume can bedetermined, whereas at infinite frequency the total fluid volume (extra-plus intra-cellular) can be measured.

The calibrated MUFI instrument has indeed been able to measure the intra- and extra-cellular water contents successfully. As a result of this success, NTE has also investedits own money in the development and certification of a commercial product, which isa derivative of the MUFI instrument.

At present, those physicians dealing with healthy people such as sportsmen, fighterand test pilots, people requiring diet control, scientists performing bed-rest studiessimulating microgravity conditions, etc., are potential customers for the commercialMUFI instruments. Calibration of the MUFI technique for different diseases will bestarted in the near future.

The total investment to date in the MUFI project by PNE (Plan Nacional del Espacio ofSpain), ESA and NTE amounts to 1.3 million Euros. The expected sales, on the basis ofconservative assumptions by NTE are: 180 kEuros in 2001, 420 kEuros in 2002, and780 kEuros in 2003.

In addition to the MUFI instrument, NTE has developed a spin-off for biomassmonitoring, from an ESA TRP study on life-support systems. It has also developed adevice to measure the quality of meat, based upon the electrical-impedancespectroscopy technique discussed above. This particular development has beensupported by the European Union.


measurement. All of thesestandard services to theexperiment modules wereaccommodated in the Texus Service Module. Kayser-Threde developed, maintained,and upgraded these Service Modules and provided the computer-based electricalground checkout equipment, as required for the integration and monitoring of theTexus payload.

From the start of its space-research-related activities, which cover some 30 years,Kayser-Threde has looked for terrestrial applications of its space know-how. This hasbeen derived from work on the development of scientific facilities, satellitesubsystems, and elements of space transport systems, as well as the activities in theTexus Programme. It has found those applications mainly with the German railwaysand in the car industry. Today, about 50% of Kayser-Threde’s business is independentof any space programme, but is all derived from the original space activities. It nowcovers high-speed data acquisition, coding, handling and transmission systems, GPS-based location techniques for rail, car, and truck traffic, and crash-test facilities.

Kayser-Threde is a major supplier to the German railway system of the autonomouselectronic supervision and control equipment needed to control the electrical energysupply and distribution.

The value of Kayser-Threde’s space-derived spin-offs in 1999 was about 6.5 millionEuros, and averaged about 5 million Euros per year over the period 1994–1999.Kayser-Threde expects the non-space part of the company’s activities to increase stillfurther in the future.

3.2.13 Body-Fluid Monitoring with Multi-Frequency Impedance Measurements

In early 1995, the Spanish company NTE received a contract from ESA covering ‘Body-Fluid Monitoring with Multi-Frequency Impedance Measurements’. This contractincluded the development of five units of the Multi-Frequency ImpedanceMeasurement System (MUFI), capable of measuring the distribution of intra- andextra-cellular fluid in the whole body and in segments of it such as the head, thorax,abdomen, arms and legs.

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Figure 3.2.8. Crash-testingequipment, one terrestrial

application of Kayser-Threde’sexpertise in system

measurement and datamanagement for the Texussounding-rocket payloads

The unit cost of the locometer platform, including software, amounts to 70 kFF. Theposture-analysis platform costs 56 kFF. SATEL’s recent and projected sales figures areas follows: 7/98–6/99: 70 000, 7/99–6/2000: 210 000, 7/2000–6/2001: 400 000and 7/2001–6/2002: 610 000 Euros.

3.2.15 Future Developments

Besides those applications and technology transfers that were described above andare summarised in Table 3.2.2, a number of other space-derived commercial applicationswere identified. These are presently either at an early stage of commercialisation or areat the component level, making an assessment concerning their future commercialprospects more difficult. A number of them are outlined below.

- Shape-Memory Alloys for Implanted Medical Devices

Previous developments of prototype equipment for use in space, undertaken under aseries of contracts awarded by ESA to Brunel Institute for Bioengineering (UK)facilitated the spin-off of Anson Medical Limited, a UK-registered companymanufacturing implanted medical devices.

The specific technology associated with the development of space equipmentfocussed on the dynamic properties of Shape-Memory Alloys (SMAs). The rationale forthe use of these materials was to try to simplify the complex mechanical devices, such as actuation mechanisms, that were to be used on-board ‘Biosample’, anexperimental plant-research facility. The Biosample module was originally intended asan automated life-science facility for the unmanned European Retrievable Carrier(Eureca).

Shape-memory alloys were used for:– optical-mirror actuation– a plant-cutting actuation mechanism– a miniature rotary-drive engagement mechanism, to shield delicate electro-

mechanical devices

Anson Medical Ltd. produces implanted medical devices for use in cardiovascular andorthopaedic surgery and treatment. These devices are made wholly or partly fromshape-memory alloys. The products currently under development and undergoingtrials are vascular stents, vascular stent-grafts, and endoscopic instruments forcardiovascular intervention and orthopaedic trauma.

The sales of Anson Medical should be about 900 kEuros in 2001 and are expected toincrease rapidly in subsequent years.


3.2.14 Posture Platform and Locomotion Measurement System

Within the framework of Franco-Russian missions to Mir, the Laboratoire dePhysiologie of the Medical Faculty of Toulouse Rangueil (Profs. Bessou, Depui andMontoya) has conducted research on human balance, posture and locomotion inmicrogravity, using pre- and post-flight measurements as a reference.

Balance regulation involves the transfer of signals from specialised nerve sensors tothe central nervous system, with the aim of maintaining good balance and harmonyof body movements (see Section 2.1.6).

In order to measure and analyse the postural regulation of a standing subject, thecompany SATEL, in co-operation with the Laboratoire de Physiologie, has developed a‘force-platform’. This force-platform enables the recording of statokinesigramme plotsof successive positions of the centre of pressure exerted by the subject’s feet on theplatform with respect to a reference axis. These measurements are performed with‘eyes open’ and ‘eyes closed’, because the ability of individuals to balance in staticconditions is quite different in the two cases. A computer associated with the force-platform displays the statokinesigramme in real time on a screen and makes anassesment of the subject’s ability to maintain orthostatic balance.

This balance platform is now increasingly used in the clinical evaluation of posture inthe fields of neurology, ENT, gerontology, traumatology, sports physiology and physio-therapy. A large portion of the population has posture deficiencies or disturbances.

A second apparatus, the ‘mobile platform’, was also developed by SATEL, in co-operation with the Laboratoire de Physiologie at Toulouse. It measures and analysesthe dynamic-balance function of human subjects during walking. This mobile platformenables therapists to identify the patient’s sector of balance deficit using visualisationof the measurements. Based on these measurements, the therapist can develop for thepatient a physiotherapy programme using postural biofeedback. Simultaneousrecording of both feet during human walking is used for the analysis of locomotion,with the aim of accurately assessing spatial and temporal parameters of thatlocomotion and identifying deviations from normal locomotive behaviour.

- Economic Aspects

The company SATEL was founded in 1981 with the objective of supporting thedevelopment and promote the utilisation of medical equipment. As far as therapeuticapplication of the SATEL posture and locomotion diagnostics and therapy instrumentsis concerned, the French Social Security Dept. has recently approved coverage of up to10 sessions (at 100 FF each).

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The Mamagoose is a suit for babies, whereas the RIP suit was specifically designed forastronauts. It measures rib-cage and abdomen movements during respiration and itgives an alarm if these movements stop. The Mamagoose had to be made watertightand designed to limit the possibility of frequent false alarms. Completion of theMamagoose development and testing effort will require up to two years.

It is estimated that the US market for FDA-approved Mamagoose suits would be about10 000 units per year, with a substantial market also in Europe.

- A Bioreactor for Biomedical Applications

Prof. A. Cogoli of the Space Biology Group at the ETH in Zurich (CH) has worked since1977 on gravitational and space-biology subjects. In particular, he has worked on cellbiology (signal transduction, cell differentiation and proliferation), immunology,bioprocessing and technology in space. He participated as Principal Investigator infive Spacelab missions, several sounding-rocket flights, Mir, Foton and Spacehab, andwill be the PI on the Biopack STS-107 mission in 2002. The ETH team has developedthe following hardware for space missions:

– Cell-culture incubators and cell-culture flasks.– Blood kits and immuno-test kits for immunology experiments in microgravity.– Mini-bioreactors with automatic medium replacement.– Bioreactors for Biorack Type-2 Containers.

Of this space research hardware, the Space Bioreactor for Biomedical Applications isthe most application-oriented development. However, it is expected that it will requirea further five to ten years of research in space and on Earth for it to become acommercially viable product. This project was selected as an ESA MicrogravityApplications Project (MAP) early in 1999. The Bioreactor project team, led by Prof.Cogoli, consists of five co-investigator teams and the company Sulzer Medica ofWinterthur (CH).

The production of artificial tissues and organ-like structures is one of the mostinnovative and timely technologies. Understanding of the molecular and biologicalmechanisms regulating the growth and survival of such structures is a necessaryprerequisite for medical applications. It is believed that microgravity may contributein two respects to progress in this field. Firstly, it is a useful tool for investigatingimportant biological events at the cellular and molecular levels (e.g. signal transduction,genetic expression and cell proliferation) from a new and non-invasive standpoint. (i.e.avoiding inhibitors or other biochemical agents). Secondly, low-g conditions may alsofavour the mass production of cells, by obtaining higher cell densities per unit culturevolume, and enable smooth cell-cell aggregation and three-dimensionalorganogenesis, in the absence of gravity or of damaging sheer forces due to agitation.


- Back-Pain Diagnosis and Therapy Device

Contrary to expectations, most astronauts have suffered from back pain whilst inspace. In order to try to determine its origin, Prof. Baum of the DeutscheSporthochschule, Cologne, developed a six-channel ultrasound device. Thisinstrument measures the distances between eight electrodes (each with oneultrasound receiver and one transmitter) on the skin. The information is recorded witha sampling frequency of 1 Hz over 56 hours (accuracy better than 1 mm) for laterevaluation, in terms of body attitude, muscle movements and recommendations fortherapy measures.

In the experiments, both distance changes at selected points of the back and theelectric potentials (EMG) were measured simultaneously. The resulting conclusion wasthat back pain is mainly due to insufficient movement of back muscles. It is not dueto spine length changes or atrophy of spinal discs, as had been assumed originally.The pain results from an isometric contraction of low intensity of muscles on bothsides of the spinal column if the body does not move sufficiently. Bed-rest studies haveconfirmed this conclusion.

Based on the experimental results of these projects on the German Mir ’97 missionand on two French Mir missions in 1998 and 1999, the small company Orthoson(Jena) has developed a very small, portable Ultrasound Sensoric Device, for which ithas obtained a worldwide patent. All clinical tests are complete and were successful.However, up to two years are estimated to be needed to develop a commercial unit,which will also be able to provide instructions for therapy countermeasures (i.e.defined muscle exercises).

In the industrialised world, about a third of all sick-leave days, and one third of all earlyinvalidity cases, are related to back pain. It is estimated that in Europe, where theannual medical and rehabilitation expenses exceed 1000 billion Euros, about 20% ofthe costs are spent on back-pain-related medical treatments and rehabilitation.Consequently, an instrument such as this is likely to find a significant market.

- ‘Mamagoose’, a Monitor to Reduce the Incidence of Sudden Infant Death Syndrome

This spin-off is derived from the ‘Respiratory Induction Phethysmograph’ (RIP)experiment of Prof. Paiva (Université Libre de Bruxelles). The space version of it wasdeveloped by the company Verhaert Design and Development. It was first flown as anelement of the large ESA human physiology research facility Anthrorack, on the D-2Spacelab mission in 1993. The clinical tests on the RIP-derived ‘Mamagoose’ havealready been performed.

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temperature gradients in the melt. Dedicated microgravity experiments led to themeasurement and the characterisation of the Marangoni effect. Theoretical studies byProf. Ratke (DLR, Cologne) led to the validation of numerical models and finally to thepossibility of controlling the direction and velocity of this Marangoni-inducedmigration.

The next step was the use of this knowhow to counterbalance – in productionprocesses on Earth – the gravity-induced sedimentation of the higher density dropletsby a reverse Marangoni migration. By applying this balancing method in terrestriallaboratories, it was possible to obtain homogenous dispersions of particles of a softmetal (which provides the lubrication) in the matrix of a hard metal.

The application of such new and better lubricating materials in cars would have majoreconomic benefits in terms of the lifetime of the bearings and of fuel consumption,since many sliding bearings are employed in every car. The DLR Space SimulationInstitute is trying to obtain a European Union research contract to cover theinvestment needed to procure a Strip Cast Machine (1 million Euros). This would beused for the optimisation and model validation of different bearing materials, and toobtain the automotive industry’s support for performing the expensive lifetime tests.

If the validation and further quantitative and lifetime tests are successful, there wouldbe a large potential market for this type of sliding bearing, especially in the car industry.

- Astrium-Dornier Spin-Offs

Of all the European space companies, Astrium-Dornier was in the past the one mostinvolved in the development of microgravity experiment facilities for the ESA andGerman national microgravity research programmes. In addition, Astrium-Dornierwas for many years the main contractor for the ESA Technology Research Programme‘Space Materials Sciences’. This involvement, in co-operation with a number ofEuropean subcontractors, has led to several technological advances and componentimprovements, which have already or which will find spin-off applications in variousnon-space industrial fields.

Examples of such applications are:– Miniquarium, derived from Biorack, is outfitted with various integrated and individual

micro-sensor packages for pO2, pCO2, pH, nitrate, glucose, flow, relative humidityand temperature. In addition, there are gas/water/nutrient/medium exchangers,feeding systems, micro-pumps, and an optical observation capability, i.e. allcomponents that are useful for advanced bioreactors.

– A novel technique for detecting the solid/liquid interface in solidification processes,developed in cooperation with Access eV (Aachen) and the University of Leipzig. Themethod is based on the application of longitudinal, guided ultrasonic waves,


Sulzer Orthopedics is a medical-device company that is investing heavily inbiotechnology to develop the next generation of implants, i.e. implants leading totissue repair and regeneration. Their R&D programme comprises biological implants toregenerate meniscus and articular cartilage in the knee, as well as to develop growthfactors for the induction of new bone. Sulzer Orthopedics’ expertise lies especially inproviding implants containing autologous cells of the patient.

The first phase of applied research focuses on the understanding of biologicalprocesses of cartilage tissue formation in-vitro, followed by the application of thisknowledge to the industrial process of cartilage production. It is expected that theadvanced bioreactors to be developed will form the basis of automatic cartilageproduction. The automatic process will also be used to grow organs such as liver,thyroid, pancreas, etc.

The implants are in-vitro-developed organ-like structures that are implanted into thebody, where they then develop to fully functional tissue organs.

The company owns a patent on the production of cartilage in-vitro, using free cells.The literature demonstrates the importance of microgravity for in-vitro cartilageproduction (improved 3D growth), due to the reduced mechanical load in microgravity.The bioreactor will allow the production of mass cell cultures for pseudo-tissues andpseudo-organs by in-vitro organogenesis. The use of viable autologous cells in thebioreactor will allow the utilisation of the body’s own repair and remodellingmechanism.

Tissue engineering is an expanding field of medical research, which will potentiallylead to relevant clinical applications in the near future. The present world market forartificial tissue-engineered products amounts to about 5 billion Euros, and isincreasing by about 25% per year.

- Novel Bearing Alloys for Car Engines

On Earth, a number of alloy systems exhibit two immiscible phases when they areliquid. The fact that each phase has a different density can lead to separation bygravity-induced sedimentation, both before and during solidification. What is neededfor applications is a homogeneous distribution of the two phases. In the case ofmaterials for bearings, a soft metal in the matrix of a hard metal is desired.

It was originally assumed that, because of the absence of sedimentation inmicrogravity, the solidification of such alloys under those conditions would result in ahomogeneous distribution. That did not occur, however, because of the effect of agravity-independent mechanism called ‘Marangoni migration’. This migration isdriven by interfacial tension gradients on the surfaces of droplets, caused by local

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supplied from a transducer/receiver at the cold end of the sample. The position ofthe solid/liquid interface is determined by a time-of-flight measurement for thefraction of the wave that is reflected at the interface. The resolution of this methodis better than 0.01 mm, which is ample for terrestrial and space solidificationresearch. At present this technique, derived from an ESA TRP development, is usedby the companies RWE and Heidelberger Druckmaschinen, and by the glass industry.

– The use of Vacuum Insulation Panels (VIP) as structural wall elements with stronglyincreased insulation performance. Astrium-Dornier has made the Refrigerator FreezerRacks for ESA for use on the International Space Station, for which such VIPs havebeen developed. The VIPs thermal conductivity is about 10 times lower than that ofconventional insulation. VIPs are already utilised for high-end commercial freezersand allow energy savings of up to 30% compared to conventional designs. The VIPspin-off is especially interesting for rail, ship, road and air transportation.

A number of further potential Spin-Offs from space fluid-physics experimentation arelisted in Table 3.2.1.

- Telemedicine and Health-Telematics

The European Commission defines ‘Telemedicine’ as a specific part of telematicsapplication for healthcare or ‘Health-Telematics’, the latter term being derived from thecombined use of telecommunication and informatics technologies in the healthcaresystem in general.

These telematics technologies find application in the medical services, as well as in theassociated support services. They will therefore be used by doctors, as well as bynurses, pharmacists and other ‘health agents’. Applications will include the directmedical treatment processes as well as the prevention, general care and rehabilitationactivities. Telemedicine in this context is understood to be the use of health-telematicstechnologies in the direct care process, in situations where the patient is located at adistance from the source of the requisite medical expertise.

Health telematics is used for medical diagnostics and consultation. A simpleapplication would be the consultation of on-line computer databases, such as a searchfor abstracts of publications on relevant medical cases. The advances in the capacityof today’s communication links and technology, via satellites or fibre optics, allow theprovision of medical services to patients at remote sites where no medical experts areavailable. The wide-bandwidth transmission of digital signals, in conjunction withcomputer services, allows the transfer of ECG, digital X-ray images, and high-resolutionmotion pictures from remote sites to medical centres for diagnosis and consultation.The most relevant applications of video-telemedicine are those that do not requireface-to-face contact between the physician and the patient.

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Table 3.2.1 Potential Spin-Offs from Space Fluid-Physics Experiments

Name Original Microgravity- Potential Non-Space Potential for NewRelated Project Application Commercial

Application

Astrium/Dornier Bubble, Drop and Particle Car engine control Sports- and racing and subcontractor Unit (BDPU) cars (BMW)Ferrari SpA TC3 Mini Gas Compressor

Astrium/Dornier Bubble, Drop and Particle Advanced temperature Ultra-small and + consultant Unit (BDPU) sensoric instrumentation fast object/media TU Munich TC3 Mini Thermistor (gas/liquid applications) instrumentation

Sensors

Astrium/Dornier Bubble, Drop and Particle Crystal growth from liquids, Miniaturised ultra-+ subcontractor Unit (BDPU) diffusion and chemical precise process-Laben SpA TC1/7 Liquid Separation processes control device

Sheets

Astrium/Dornier Bubble, Drop and Particle Binary physico-chemical Liquid/liquid and+ subcontractor Unit (BDPU) processes with trapped gas liquid/gas separationOfficine Galileo TC2/6/8 Gas & Liquid bubbles of liquid drops without loop

Extraction System

Astrium/Dornier Bubble, Drop and Particle Advanced measurement of Chemical process+ supplier Univ. Unit (BDPU) liquid flows (esp. LDV and control and two-phaseLibre Brussels TC1/3/7 Liquid Tracers PIV applic.) using silvered flow

nanospheres

Astrium/Dornier Holographic Optics Compact/automatic 3D flow and object+ subcontractors Laboratory (HOLOP): holographic camera for measurements inKayser-Threde Thermoplastic Camera industrial applications research and industryand Labor Steinbichler (liquid/gas processes,

object deformation)

Astrium/Dornier Holographic Optics Advanced thermal insulation Railway, road, aircraftLaboratory (HOLOP): (with hot/cold application transportationISIS-GVI (Glass Fibre Vac. Isolation) potential; also for rough Passive transport

chemical environments) (20x lower heat conduction)

Astrium/Dornier Refrigerator/Freezer Rack Advanced thermoelectric Mobile thermal-+subcontractor (RFR) coolers for mobile conditioning applications,Nucletron/Marlow Thermoelectric Cooler applications (e.g. ships, noise and vibration-

Assembly aircraft, trucks) or high sensitive thermaldemands concerning noise, conditioning and low-vibration, reliability temperature cooling

Astrium/Dornier Refrigerator/Freezer Rack Humidity management, Enhanced cooling device+subcontractor (RFR) within non-gravity defrostingVerhaert Defrosting and Humidity environment or without (refrigerator/freezer)

Management active pumps

Union. Over the past 7 years, DLR has acquired a co-ordinating and moderating role inthe process of introducing telematics into healthcare systems.

In addition to these telemedicine collaboration projects, which are supported by theG-7 countries, WHO and the European Union, there is a very interesting initiative atGerman national level. It concerns the development of a Health Telematics Platform,with the establishment of virtual electronic health records and electronic prescriptionsfor regional healthcare networks that will finally merge into a federation of networkswithin Germany and beyond. Presently, negotiations on the implementation of suchsystems are being undertaken with communication and e-business providers, such asDeutsche Telekom.

3.2.16 Spin-Offs: Impact on Jobs and Company Creation

Another type of benefit derived from ESA and national microgravity researchprogrammes is the creation of some 20 small companies in the last two decades invarious European countries. These have subsequently used their acquiredmicrogravity-related knowledge to broaden their activities into other space disciplinesand into non-space industrial developments. There were a further 20 existing Small-and Medium-sized Enterprises (SMEs) that have extended their activity strategy toinclude microgravity developments and to exploit them in their terrestrial branch orto create spin-off companies for this purpose.

The following is a non-exhaustive list of these new or reoriented SMEs and the largerspace companies where new jobs have been created due to their involvement inmicrogravity work:

Belgium: Chevalier Photonics, Lambda-X, Logica, OIP, Verhaert, Trasijs SpaceDenmark: Damec, InnovisionFrance: Aerospatiale, Cadmos, Comat, Diatecnic, DMS, Matra, Medes, Medilink,

Novespace, SEP, Soterem, Vermon, 3ISGermany: Access, AICON, Astrium, Chronos Vision, DLR Musc, EPSa, Intospace, KT,

OHB, Orthoson. SMI, ZARMItaly: Alenia, Carlo Gavazzi, Ferrari, Laben, Mars, Officine Galileo, Tecno SystemNetherlands: Bradford, Comprimo, FokkerNorway: Prototech A/SSpain: Crisa, NTE, SenerSweden: Saab Ericsson Space, SSCSwitzerland: CIR, Contraves, ETEL, HTS, MecanexUK: Anson, BAe, BIB, Sira.

It is estimated that as a consequence of microgravity-related developments and theirterrestrial exploitation in these smaller companies, and in the large space companies


Telematics is considered to be the key to overcoming the dilemma that all healthcaresystems in the developed countries are facing: i.e. increasing demands being placedupon decreasing or stagnating resources. The widespread use in the future oftelematics should improve, or at least maintain, the quality of health care for thegeneral population. It can provide increased access to medical specialists, reducetransportation costs and increase the overall cost efficiency.

Telemedicine can allow home-monitoring of patients who are still recuperating afterearly discharges from expensive stays in hospitals after surgery. It allows home-monitoring of old people, at a time when they are forming an increasing portion of thepopulation. Such a monitoring system will enable the elderly to live longer in their ownhomes, under conditions of ‘controlled, self-determined autonomy’. Telemedicine is a newfield that provides major opportunities. It has a large market potential, running tobillions of Euros, once general acceptability by physicians and patients has been achieved.

The two leading nations in manned spaceflight, the USA and the Soviet Union/Russia,have used tele-monitoring and video-conferencing to monitor the health of theirastronauts. With the start of regular, long-duration, manned missions on theInternational Space Station, and later of manned missions to Mars, it will be essentialto develop autonomous decision-support systems with the combined use oftelemedicine and robotic devices/instrumentation. Even more than in the past, thespace programme will have a lead role in the development of advanced telemedicineand the qualification of the associated new technologies. Other potential applicationsof this new healthcare technology include its use in battlefield surgery, duringwilderness expeditions, and in connection with emergencies during air and seatransportation.

In the early 1990s, the Health Telematics and User Support Division of the DLRInstitute of Aerospace Medicine carried out the Baseline Data Collection (BDC) for theAnthrorack human-physiology experiments for ESA. (Anthrorack was ESA’s largest life-sciences facility, flown on the German D-2 Spacelab mission in 1993).

Based on this BDC experience, the DLR team has continued to use and to improveinformatics and telecommunication technologies for applications in healthcareactivities. They became involved in a number of telemedicine research anddevelopment projects, nine of which were supported by the European Union in the 4thand 5th Framework Programmes in the period 1996–2001. In addition, DLR’stelemedicine projects were promoted by government organisations such as theFederal Armed Forces (Deutsche Bundeswehr), and industrial organisations such asDeutsche Lufthansa.

The total third-party funding for DLR’s telemedicine projects in this period was morethan of 2.5 million Euros, of which 0.7 million were contributed by the European

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Coming back to the selected spin-off instruments listed in Table 3.2.2, most of themwere originally built to monitor the health of astronauts or to perform biologicalexperiments in space. These instruments can often be used, with some adaptation, inthe bio-medical equipment market. A further feature of the ‘Microgravity Spin-Offs’ isthat most of them were derived by the smaller firms, rather than by the larger well-known space companies. For the latter, the development of microgravity researchfacilities represents only a ‘small project’, from which the company management isless interested in deriving terrestrial spin-offs or performing technology transfers.Their ‘core activities’ lie in spacecraft development and integration, and missionoperations. Life- and materials/fluid-science activities and the associated hardware areoften considered to be too far from their company’s core competences and objectives.

However, the large space companies did acknowledge deriving some benefits from thesmaller microgravity projects. These included the interaction with a new scientificcommunity, interdisciplinary projects, the application of new principles oforganisation and the management of new small companies as subcontractors, withdifferent areas of knowledge and competences required for life and physical sciences,and with cross-fertilisation between the science teams, the small companies and thelarge space firms taking place.

For their part, the smaller companies involved in the development, production andmarketing of spin-offs often had to cope with other difficult aspects. These includedtrying to obtain funds to build a production line or to find an appropriate commercialpartner to sell the spin-off product in a given niche market. There are also sometimesfears that large non-space companies would either take them over or fightcommercially against the success of a competitive instrument in ‘their’ market.

Another feature of several small companies was that they accepted the developmentof a space instrument only if they could exploit their existing terrestrial technicalknowhow to a significant degree. These small companies always had a terrestrial spin-off of the space instrument in mind, and this demanded low unit costs to make itsellable on the terrestrial market. This in turn led to the application of existingterrestrial technology and fabrication methods, which had to be upgraded to meetspecific space requirements, such as reliable functioning in a hostile spaceenvironment, and to survive the launch phase. This was a kind of ‘spin-in’ from normalterrestrial techniques, which made the space products less expensive and the laterspin-off more competitive on the terrestrial market. It was a time- and cost-effective‘spin-in – upgrading – spin-off’ mechanism, which avoided unnecessary duplication ofdevelopment effort and investment.

There are several potential future spin-offs in the wings, such as the BackpainDiagnostic and Therapy Device and the Bearing Alloys for cars, which have very largepotential markets. Yet it remains to close the financing gap between the prototype and


such as Aerospatiale, Alenia, Astrium and Matra, almost 1000 new jobs have beencreated. In addition, there are several hundred scientists in European universities andresearch institutes who are involved in microgravity research work.

3.2.17 Conclusions

As was already mentioned in the Introduction to this chapter, the results of this specialreview are not based on a comprehensive and systematic evaluation of the technicaland economic aspects of all microgravity spin-offs. They are based only upon a limitedsample of identified projects that are just entering the commercial market, mainly inthe medical service and research sectors. There are many other developments,especially at the component and materials-processing levels which, due to thedifficulty in identifying and assessing their economic impact, have not been addressedin detail in this review. Nevertheless, whilst concentrating on spin-offs at theinstrument level, this review has shown clearly that large sales benefits have alreadybeen achieved and that the market expectations for the coming years are excellent.

The main results of the review are summarised in Table 3.2.2. From this table and theinformation provided in the various sections on the individual spin-offs, it can beconcluded that the market for these selected examples of ‘Microgravity Spin-Offs’ willbe:– 50–60 million Euros in 2001, and– 90–100 million Euros in 2002

with a likelihood of increasing still further in subsequent years.

These figures do not include the important aspect and value of knowledge transfer toterrestrial production lines. Such transfers may be to the space companies, often withnew daughter companies being created for the production and marketing of suchspin-offs. They may also be to other companies, to which both knowhow and newtechnology has been transferred. In this context, it is important to mention that themajority of the companies in this survey stressed that what they learned in their spaceprojects in terms of scientific principles, methods and technical and managerialknowhow was particularly important as a basis for future non-space technicaldevelopments. This is especially the case in the field of materials/fluid sciences, wherein general the sophisticated and expensive space equipment, such as furnaces or fluid-science facilities, cannot be directly used in the terrestrial factory. However, theexperience acquired in terms of novel processing and control techniques is relevant.So too is the knowledge concerning the design, development and qualification of novelequipment with high reliability and reproducibility properties. These are considered bythe large space companies to be of very high value, and by the smaller companies asvital for the success of their non-space activities.

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the necessary follow-on development, to set up a production line, and to seek anintroduction into the terrestrial market.

In conclusion, it can be said that this ‘Microgravity Spin-Off Review’, whichconcentrated on just a small sample of spin-off facilities and equipment and theireconomic aspects, has yielded an unexpectedly large harvest. The systematicpromotion of technology transfer and support for the creation of commercially viableproducts in the future is therefore fully warranted. Without such promotion, severalidentified economically interesting developments might not find their way to themarket. The approach adopted within the European Union’s Framework Programmeis a good example of the promotion of and support to small and medium-sizedcompanies.

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Name and Type of Spin-Off/ Company/ Original Space Unit Price Present and Future Assessment of Technology Transfer Institution Project or of Spin-Off Annual Markets Overall Economic

Mission (MEuro) Sector

1. Ocuton S: Selftonometer Prof. Draeger Tonometer on D-1, 1 kEuro 99/00: 1000/1.0 2M units in for Glaucoma Patients EPSa (Jena, D) D-2 and Mir 2001: 5000/5 Europe (=2BEuro),

2002: 10000/10 several millionunits in USA

2. Osteospace: Device for Medilink/DMS BDM on Euromir 18 kEuro 99/00: 100 units/1.8 Ultras. Bonethe Diagnosis Started by ’94 and ’95 2001: 150 units/2.7 Densitometerof Osteoporosis MMS/Gip- 2002: 200 units/3.6 Market in Europe:

Ultrasons 2500 in 99, 5000 in 00.In world: 600 MEuro/year

3. Video Oculograph Senso Motoric VOG on D-1, D-2 65 kEuro 99/00: 4 World Market:for Eye Clinics (VOG) Instruments and Mir Missions 2001: 4-5 11 MEuro, 35% of

(Berlin, D) 2002: 5 of this covered by SMIExtension with3D-VOG

4. Sterilite: an Ozonizer Box Bradford Biolab for 2.3 kEuro 2000: 1000 units/2.3 100000 totalfor Disinfection/ (Heerle, NL) Columbus Lab. 2001: 2700 units/6.2 market potentialSterilisation on ISS 2002: 4400 units/10 in Europe + USA,

clinics, doctors,dentists, andlaboratories

5. Triple Containment Bradford 7 Biorack + 100–150 2000: 8 units/1.6 Cancer + otherGlovebox for Medical (Heerle, NL) several other kEuro 2001: 60 units/6 biomedical Research and Services missions 2002: 200 units/30 research, artificial

insemination (200 unit batchplanned for production)

/......

Name and Type of Spin-Off/ Company/ Original Space Unit Price Present and Future Assessment of Technology Transfer Institution Project or of Spin-Off Annual Markets Overall Economic

Mission (MEuro) Sector

6. Flat Swinging Heat Pipes Bradford ESA-GSTP and 0.4 kEuro 2002: 6000 units/ Use in civil andfor Aviation Industry (Heerle, NL) Atlid Satellite 2.5 per year with military aircraft

Programmes + increasing tendency (JSF) 3000 planes,Others 20 units in

4 years

7. Respired Gas Analyser for Innovision Anthrorack - D-2 15 kEuro 2000: 10 units/0.15 Very largeCardiopulmonary Diseases (Odense, DK) Euromir ’95, (70 kEuro) 2001: 300 units/4.5 medical market,(Breath Analyser) Spacelab + ISS 2002: 600 units/9 heart and lung

sector

8. Dry Toilet, Waste 3IS Rhesus Res. 0.2 kEuro 2000: 400 caravans, 600 buses, Management Device (Toulouse, F) Progress, Bion (caravans) 50 buses/0.2 20000 caravans

Transfer to Missions 2.0 kEuro 2001: 2000 caravans, + boats + Actia (buses) 200 buses/0.8 customs ports

2002: 3000 caravans, (10 units, 300 buses/1.2 0.5 MEuro total)

+ potential for small planes +clinical version indevelopment

9. 3D-Eye Tracker, for Chronos 3D-VOG on D-2 35 kEuro 99/00: 30 units/1.0 Marketing viaStrabismus and Other Vision/ and Mir missions 2001: 70 units/2.5 Skalar Medical Eye Surgery FU Berlin (D) (NL) and IVP (S)

10.Ultrasonic Components Vermon (F) PVH, As de Coeur N/A In 1999, the spaceSensors, Probes, etc. Imasonic (F) (CNES), Bone (differs for derived components

Ultrasons (F) Densitometer each had a value of 5.7(ESA) company) 2000/01, not less

than 5.7 annually

11.Pro-Cam3, a 3D AICON ESA Techn. Res., 65 kEuro 2000: 10 systems/0.7 Strongly growingPhotogrammetic Mobile (Braunschweig, Progr. Studies for average 2001: 50 systems/3.3 market in car, Measurement System for D) AFPM on D-2 (annual increase 30%) airplane and shipIndustrial Quality Control industry, at least

until 2005

12.Body Fluid NTE ESA Techn. 10 kEuro 2001: 0.2 Used by Monitoring using (Barcelona, E) Research Progr. 2002: 0.4 physicians Multi-Frequency Studies for 2003: 0.8 treating Impedance Measurements Human Physiology sportsmen,

pilots, people ondiets, and by researchphysiologists.

13.Posture Platform and Satel French missions 8.5 kEuro 2000: 0.3 Neurology, ears/Locomotion Measurement (Toulouse, F) to Mir, Research Post. Platf. 2001: 0.5 nose/throat,System at Physiol. Lab. of 10.7 kEuro 2002: 0.7 gerontology,

Univ. of Toulouse Loc. Plat traumatology,sports physiologypsychotherapy

14.Crash-Tester Data Kayser-Threde Texus Sounding Varies, 1994-99: 5/year Growing market Acquisition System for Car (Munich, D) Rocket Electronic because 1999: 6.5 in car industry,Industry – Railway Check-Out system 2000 onwards: 60% of railwayElectric Supply Control Equipment adapted to 6.5/year or more needs, constant

specific needs market

Table 3.2.2. Selected Spin-Offs from Microgravity Life- and Physical Sciences

Table 3.2.2. Selected Spin-Offs from Microgravity Life- and Physical Sciences (continued)

Evidently, a commitment from industry to take over a substantial part of the operationand utilisation cost of the ISS can only be seen as a long-term goal. In order to shorten the period of time required to reach that goal, suitable means have to beestablished to facilitate the increasing involvement of industry. These are presentlyunder discussion among the ISS partners, i.e. the space agencies, space industry andthe scientists interested in the procurement of applied research for industrialpurposes. It is obvious that a suitable background has first to be created. This should be created in an ESA-supported programme in which the advantages ofmicrogravity can be demonstrated through experiments based on the requirements ofindustry.

The programme concerned is the Microgravity Application Promotion (MAP)Programme. From a number of proposals received by the Agency from co-operatingresearch teams from industry and academia, a selection of projects was made by apeer-review process organised by ESA. This peer review not only considered thescientific merit of the proposals. It also emphasised the potential contribution to thesolution of industrial research problems, as demonstrated by the industrial partners inthe proposal. Such an approach forms a first but important step in the process ofachieving the desired involvement of non-space user industry in space-relatedprogrammes.

The Programme includes various aspects and it targeted the means to identify thoseof industry’s problems that could be solved more efficiently and effectively by the useof microgravity experimentation on the ISS as an additional research tool. Thisparticipation by industrial firms in selected co-operative research ventures at an earlystage will contribute to their familiarisation with the space environment. It will alsodemonstrate the potential value of the unique environment of space. In so doing, itwill assist in convincing the private sector that the benefits that accrue can justify thefinancial investment.

In order to demonstrate the possibilities of the ISS for industry, this Section will outlinethose applications that have already been identified as being of interest. It will alsoprovide an overview of the programmatic aspects intended to promote theinvolvement of industry in space-related research. Finally, an attempt will be made togive recommendations for further activities in this area.

3.3.2 Applied Research in Space of Industrial Interest

Existing experience indicates that the space environment is unlikely to be used as afabrication site for high-value products, as was too readily assumed in the earliestdays of Spacelab utilisation. Those expectations were based upon highly unrealisticestimates of the costs of space transportation and operations.


3.3 European Industry and Microgravity Experimentation

H.J. Sprenger

3.3.1 Introduction

One of the major objectives for the operational phase of the International SpaceStation (ISS) is to provide a basis for its utilisation for scientific and technologicalresearch. A large part of that utilisation will come from those disciplines that canbenefit particularly from the continuous presence of a manned infrastructure in orbit.Besides the disciplines of Space Science and Earth Observation, the Space Station willbe mainly used for experiments under microgravity conditions and for thedemonstration and validation of new space technologies.

In order to exploit the potential of this unique environment for both scientific andcommercial purposes, ESA has initiated several utilisation preparation and promotionprogrammes. Particular emphasis has been devoted to the identification and attraction ofnew users and to the supply of information, since the capabilities, the rules and theprocedures for the exploitation of the Space Station are not widely known to potentialusers. In addition to these promotional activities, the programmes need to providepractical support for the preparation and operation of experiments on the Space Station.

One of the stated intentions of the ISS utilisation strategy is to concentrate onapplication-oriented research. This means attracting the interest of industry to investin the utilisation of the microgravity environment. The long-term goal is to achieve asubstantial contribution to the operating costs of the ISS from these commercial users.According to the expected return on investment, they would be considered as payingcustomers with a shared financial commitment to the utilisation cost. However, thisobjective can only be achieved by the appropriate promotional means, which arepresently being developed within the Agency’s utilisation preparation programmes.

Recent analyses, from studies carried out by independent business and marketingexperts, have made it clear that the private sector is not yet ready to submit majorproposals for self-financed research on the Space Station. The principal reasons citedare the unacceptably high cost and risk connected with full payment for access to thespace infrastructure. However, the studies also revealed that, at present, the privatesector is hardly aware of the possible benefits that the utilisation of space would givethem in return for their investment. Moreover, the examples discussed in these studieswere considered as typical of the kind of applied research that would be subject topublic funding from European and national research funding schemes, rather thanoriginating from industry.

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surface-tension tanks needed for the liquid-fuel boosters used on telecommunicationsatellites.

A few selected examples are presented here of where knowledge and data derivedfrom microgravity experiments are believed to be contributing substantially to thesuccess of ongoing research and development aimed at advanced products andprocesses for commercial use. Based on the actual research objectives of today’smicrogravity projects and experiment results to date, the following areas have thehighest priority for experimental studies in terms of existing and possible futureinvolvement of the private sector:– thermo-physical properties of melts and other fluids– solidification behaviours of metals and alloys– crystal growth of semiconductor and sensor materials– combustion phenomena and processes– study of complex multiphase fluids– crystallisation of bio-molecules (proteins) for structure determination– cell science and bioreactor technology– human physiology and medicine.

Moreover, the recent developments in nanoscience and particle technologies point tomicrogravity being a very useful tool for the study of the self-organisation of very smallparticles into ordered and disordered structures in the absence of convection andsedimentation. Sections 2.3.8 and 2.3.9 deal with some aspects of that topic. Suchresearch is certainly relevant to applications, for example, in soot formation, thefabrication of powders having ultra-small sizes, in chemical vapour depositionprocesses and for studies of the encapsulation of pharmaceutical materials.

- Measurement of the Thermo-physical Properties of Melts and Other Fluids

In melt-processing applications such as casting, welding, etc., the heat flow and thefluid flow must be known and controlled. To understand and to predict transportphenomena by modern methods of numerical simulation, knowledge of the thermo-physical properties of the molten materials is required. A certain accuracy of theseproperties is essential for the understanding and subsequent modelling ofmetallurgical processes, thermodynamic phase equilibria and phase-diagramevaluation. Thus, precise input data have to be measured on the stable liquid and atdifferent levels of liquid under-cooling.

The demand for more accurate determinations of the thermo-physical data of reactivemetallic melts at high temperatures is a result of the experimental difficulties that arisefrom the unwanted reactions of melts with containers. For example, the viscositymeasurements reported for pure iron vary by ±100 % around the average. Also, arecent survey of available data for the surface tension of pure liquid metals


More realistically, it can now be predicted that the environment of space, and inparticular the ISS with its permanent manned presence, will be utilised as a researchsite where the most important property, the almost complete absence of gravity, willbe used for both fundamental and applied research. Industrial interests are likely to beserved by both of these activities, since industrial research generally containselements of basic research, e.g. if improved physical models are needed for theinclusion into numerical simulations of industrial processes involving the controlledtransport of liquid or gaseous phases.

Chapter 2 has shown that research in microgravity can indeed be used as a tool toobtain information that may otherwise not be available in a terrestrial laboratory.There is no doubt that such fundamental research can also be exploited to provideinformation that may be useful for the development of products and processes ofinterest to industry.

The individual Sections of Chapter 2 have already identified the main research areas inthe physical and life sciences in which possibilities exist for research that is useful forindustry, at least according to presently available results. Several examples have beenpresented that are either the subject of ongoing research or are potential new projects.It is clear from those that microgravity research can be applied to solve particularaspects of industrial research problems that will be of importance for increasingindustry’s competitiveness in future global markets. It is presently not clear, however,whether industry will seize upon those opportunities and demand to participateactively in space-related research.

Major applications areas can be deduced from the existing research objectives of certainindustrial sectors, in particular those that are aiming to use advanced structural andfunctional materials in new constructions, in applications leading to improvedefficiency or miniaturisation, or in biotechnological processes that are presently underdevelopment in the chemical and pharmaceutical industries. It has to be realised, ofcourse, that industry will seek the benefits from research on the ISS only if noterrestrial (cheaper) alternative means are conceivable to achieve similar researchresults.

A second potential major beneficiary from the ISS are the developers of technologiesand facilities that are designed for use in space. This is of major interest not only forspace companies, but also for suppliers who are interested in the miniaturisation or inthe improvement of terrestrial technologies for securing their function under extremeconditions (e.g. tele-operation), as well as for industry fabricating sensors, detectors,etc. These sectors would have the opportunity to achieve a competitive advantage inthe supply of products or technologies that could be used on satellites and their poweraggregates. Other examples would be the deployment testing of solar arrays in space,increasing the efficiency of cooling loops in heat rejectors, or the optimisation of the

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- Solidification Behaviour of Metals and Alloys

It is well known that most properties of metals and alloys, such as mechanicalstrength, creep resistance, ductility, and wear resistance, are determined by theirmicrostructures. The microstructural control, in turn, is very important for qualitycontrol and the design of new advanced materials for specific technologicalapplications. In particular, during melt processing, for example for casting, welding,single-crystal growth and directional solidification, the control of crystal nucleationand growth is absolutely essential. This is achieved by numerical simulation of massand heat transport in the solidifying melt, allowing calculation of the temperaturevariation (cooling curves) at each location of the processed sample or part. This, inturn, permits prediction of the actual solidification behaviour. The parameters canthen can be modified and tailored to the requirements to achieve the desiredmicrostructure. The knowledge obtained from these calculations can be used toshorten significantly the design and development time for a casting, thereby reducingthe costs that would otherwise accrue as a consequence of experimental trial and error.

The study of solidification processes, with the objective of gaining a betterunderstanding of the relationship between processing parameters, microstructure andthe resultant mechanical properties, already started during the early days ofmicrogravity experimentation. On Earth, convection has a substantial influence onfluid flow, which is responsible for the distribution of elements and particles in the meltnear the solidification front and for their degree of homogeneity after solidification.Furthermore, the thermal analysis of these processes, including multi-componentphase changes and dendritic growth, could be of interest to improve the possibilitiesfor better control of microstructure in the present models. In particle-containing alloys,the effects of gravity can lead to sedimentation and can cause increasedagglomeration, resulting in unwanted separation of the different constituents in thesolidified part. Under microgravity conditions, heat and mass transport can occur bydiffusion only, so that study of those effects can be used for a better and morequantitative understanding of separation mechanisms. This knowledge can, in turn,be used to increase the accuracy of the models used for controlling the casting andsolidification processes.

Early experiments concentrated upon determination of the influence of convectivemelt flow upon the geometry and regularity of the microstructure. With stronglyreduced convection, smaller distances between the solidifying dendrites and betweenthe eutectic phases are generally observed. Those results have confirmed thatconvective flow should be minimised also on Earth to achieve the desired fine andregular distribution that results in improved mechanical properties. These findingsalso contributed to the development of a new casting process that is already beingused for the fabrication of cast nodes in aluminium frames for automobiles and cornerfittings for aeroplane structures.


demonstrates that whilevalues are known for puremetals to an accuracy of about ±5%, the temperaturecoefficient, which is therelevant quantity controllingMarangoni convection, is onlyknown to an accuracy of lessthan ±50% for most pure metals. For alloys, and in particular for multi-componentcommercial alloys, the situation is even worse.

The thermo-physical properties of interest are melting range, solid fraction, density(thermal expansion), viscosity, specific heat, Gibbs free enthalpies, diffusioncoefficients, thermal (electrical) conductivity, surface tension and emissivity. Some ofthese data can be obtained reasonably accurately by conventional methods. However,high-precision measurements on chemically highly reactive melts and fluids at thetemperatures of interest require the application of containerless processing, usingnon-contact diagnostic tools. By eliminating the contact between the melt and acrucible, accurate surface nucleation control and the synthesis of materials free ofsurface contamination becomes possible.

Under microgravity conditions, further advantages are expected from the significantlysmaller electromagnetic fields needed to stabilise the containerless melts. This wasshown on several Spacelab missions, where the results clearly demonstrated animprovement in accuracy over terrestrial measurements, even on pure metals. This isan indication that the electromagnetic levitation technique can provide a suitableenvironment for the accurate measurement of the thermo-physical properties ofmetallic melts of industrial interest on the ISS also.

For the measurement of non-conducting fluids, the situation is different. Ifcontainerless techniques are needed to determine data for numerical simulation ofcombustion and other chemical processes (e.g. for evaporation, chemical reactions,etc.), other methods, such as acoustic levitation, have to be used. Those techniquesalso give more accurate results when applied in microgravity, because of the greatlyreduced forces required to keep the samples in a stable position.

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Figure 3.3.1. The very large spreadin measured values for the

viscosity of molten iron, indicatingthe need for better thermo-physical

data (from T. Tanaka, K. Hack,T. Lida & S. Hara, Z. Metallkunde

87, 380, 1996)

- Crystal Growth of Semiconductor and Sensor Materials

In inorganic-material crystal growth, structural perfection is one of the most importantgoals. This has been achieved to a certain degree via a better understanding of theinfluence of flow in the solidifying melt and by the ability to calculate the flow bynumerical simulation. In the last 25 years, crystal growth has advanced from an art toa science, by co-operation with fluid scientists and by the introduction of fluid-mechanics knowledge into the different growth technologies. Study of the influence ofthe different kinds of convection under microgravity also helped in the developmentof growth methods.

Experiments using microgravity to study fluid flow caused by surface-induced(Marangoni) convection (see Section 2.3.2/4), which is important for the growth ofsemiconductor crystals, were an area of intensive research during the past decades.These experiments contributed to quantifying the influence of different convectionmodes on the fluid flow, and they showed that Marangoni-driven flow can be of thesame order as flow induced by natural convection. In addition, due to the absence ofhydrostatic pressure in space, attempts were made to grow crystals from the meltwith larger diameters than is possible on Earth. This was successfully demonstratedwith GaAs crystals of 20 mm diameter, grown using a float-zone process during the D-2 mission. This was significantly larger than was possible on Earth (about 8 mm). It was, however, difficult to transfer these results to significant improvements in theindustrial growth of these semiconductor materials. Numerical simulation andaccompanying terrestrial research showed in fact that the flow during the crystalgrowth can be well controlled using magnetic fields. Moreover, the most difficultproblems causing unwanted defects in the grown crystals occur during the cooling inthe solid state. Therefore, microgravity research was dropped as a means to seekquality improvements in materials such as silicon or GaAs.

The situation is different for materials like CdTe and related compounds. These havepotential applications as highly sensitive sensors and detectors for the identificationof flaws in materials or for medical purposes, e.g. for low-dosage X-rays. So far, thesematerials have not been used in practice because the current quality of the singlecrystals is not sufficient to allow economic applications. To be able to grow material ofthe required size and quality, a better understanding of mechanisms leading todeterioration of the crystals is needed and suitable measures have to be developed toavoid those defects.

For growing large single crystals with high homogeneities, two different processes areenvisaged and are under development, both of which could benefit from research inmicrogravity. In melt growth, relevant experiments on Shuttle missions havedemonstrated that avoiding or strongly reducing the contact with container walls byapplying non-wetting conditions leads to decreasing tensions in the solid material.


Other investigations concentrated on particle distributions in metallic melts, theregularity of which is responsible for the improved quality of metal matrix composites.It was found that even without convection the particles in the melt wereagglomerating into chains and networks, which led to an unwanted viscosity increaseand to an increased risk of entrapment of impurity inclusions or gas bubbles. In thenear future, experimental investigations are planned to quantify the influence ofconvection at dendritic solidification fronts in this so-called ‘mushy zone’.

Recently, the use of magnetic fields for damping convection has been studied as aprecursor for microgravity research. This is an efficient way to control the flow of liquidmatter by avoiding unwanted turbulences. However, the interaction betweenelectromagnetic and convective flows is not well understood. It was found that eventhe physical models used in numerical simulation do not correctly describe theexperimental observations.

This is important for the development of industrial metallurgy and metal processing,in which magnetic fields are used as part of the processing itself. This leads to bettercontrol over the material properties compared to conventional technologies. This isachieved by using the different effects of electromagnetic fields, such as heating,braking of convection, stirring of the melt motion, shape control and levitation.Although the principles have been known for more than two decades, their industrialuse is constrained by several problems, even for well-established processes. This is dueto the fact that most of the existing turbulence models cannot predict or reproduce theexperimental observations in the numerical simulations. Therefore, they cannot beused to optimise the process parameters and the geometrical conditions for the use ofthe electromagnetic fields. There are clear demands from industry for a betterunderstanding of the effects of convection on the microstructure. This could be the subject of future combined terrestrial and microgravity research and wouldconsist of:

– more detailed analysis of the physics of the mushy zone, the segregation behaviourin the alloys and the related material parameters

– development of 3D numerical codes that use realistic boundary conditions– obtaining a better understanding of interface phenomena, to improve the existing

processes; this requires improved knowledge of the physics and chemistry of free-surface problems, entrapment or removal of inclusions, melt mould interaction, etc.

– development of new or more robust sensor technologies, e.g. measurement of flowvelocities or measurement of thermo-physical properties; this is necessary both forexperimental verification and testing of theoretical models and numerical simulations,and for better control of the industrial process

– definition and execution of well-defined benchmark experiments to observe specificphenomena and to validate theoretical predictions.

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best crystals of these proteins grown on Earth, were porcine elastase and gammainterferon D, bovine and human serum albumin, malic enzyme, proline isomerase andHIV-1 reverse transcriptase. Recent space experiments on human insulin (by Eli LillyCo.) gave an improvement in resolution from 2.0 (ground) to 1.4 Å, allowing the crystalstructure to be determined.

In European programmes, the efforts have primarily concentrated on increasing thebasic understanding of the influence of gravity on nucleation and growth of proteinsthrough experiments on Spacehab-1 and IML-2, in the ESA-developed AdvancedProtein Crystallisation Facility (APCF). The results, similar to those supported by NASA,showed a certain portion of crystals that were better and diffracted to higherresolution than the best samples grown on Earth. The relevant experiments aredesigned to achieve better-ordered crystals from growth in space, as well as toimprove the Earth-based methods by learning about the influence of gravity throughspace experimentation. Industrial participation focuses on proteins for structure-based drug design and protein engineering. The final goal is to developpharmaceuticals that are important in combating diseases, or for the production ofspecial enzymes that may be used as detergents in separation processes.

After about ten years of protein crystal growth research in space, the facts are that inabout 20 to 25% of the experiments under microgravity the crystals grew larger orwere better ordered than their best counterparts in terrestrial laboratories. So far, thestrongest increase in resolution has generally been observed in those proteins thatalso crystallised on Earth, but did so with a slightly disordered structure (mosaic),attributed to the presence of convection and sedimentation.

Further research will improve our understanding of the mechanisms and theconditions that lead to better-ordered proteins in the absence of convection andsedimentation. Consequently, there is a good chance that the crystallisation ofproteins with the size and structural order needed for the analysis of the three-dimensional arrangement of functional groups, can be successfully achieved in space.

There are more than a million different proteins, only a small fraction of which couldbe analysed so far for their three-dimensional structure. For industry, the mostimportant target is to determine an unknown structure as fast as possible, in order togain an advantage over possible competitors. The resolution of de-novo proteinstructures normally requires 3 to 6 months, but in particularly difficult cases up to ayear may be spent on a single protein. The ISS will provide an environment in whichprotein crystallisation can be routinely carried out with short turnaround times. Theindustrial demand will be based on the possibility to conduct a large number of trialsin parallel with extremely small sample sizes (in the micro-litre range). This requiresonly relatively small pieces of hardware, with an arrangement of hundreds of identicalchambers. To be able to obtain the structural data as fast as possible, the operation of


This, in turn, leads to a significant reduction in defects in the grown crystal. Moreover,the application of weak rotating magnetic fields is responsible for the setting up of alaminar flow, which favours relatively uniform transport of the components in the melttowards the advancing solidification front.

- Growth of Protein Crystals and of Other Large Biomolecules

Protein crystallography is a method of determining the three-dimensional structure ofproteins by the analysis of X-ray diffraction data. The results provide the keys for basicstructure studies, drug design and protein engineering. Crystallisation of proteins andnucleic acids with the required homogeneity and size is therefore one of the key issuesfor the analysis of the three-dimensional structure and the determination of functionalgroups of proteins and similar large organic molecules.

The growth of such crystals in a terrestrial laboratory is, in many cases, a difficult oreven impossible task. Though a number of experimental techniques have beendeveloped, they often fail to produce crystals of sufficient size and quality. It has beenobserved that several different parameters influence the crystallisation process, one ofthem being the action of gravity. Though the exact mechanisms are still not known, itis believed that the nucleation and growth processes suffer from the presence ofconvection and sedimentation. Further problems stem from the non-reproducibility ofexperiments and the lack of rational (empirical) methods to predict under whatconditions a certain protein may or may not crystallise.

Positive results on early Spacelab missions stimulated worldwide attempts to carryout systematic experiments in the field of protein crystal growth. Those experimentspartly involved the participation of a number of pharmaceutical companies,particularly in the United States. In Europe, several attempts were made to growprotein crystals on unmanned spacecraft, with a view to commercial production. Forcertain substances (especially lysozyme, a generally accepted test substance), thegrowth of larger, more uniform crystals with higher order at the molecular level ispossible in space.

All of the various methods used are believed to benefit from microgravity experiments.The parameters that affect the crystallisation of proteins are diffusion rate, convection,density (sedimentation) and wall/interface effects. The goal is to find conditions thatfavour the nucleation of a small number of crystals, which should then grow to largersizes and with greater crystallographic perfection (see Section 2.3.1).

Growth experiments by the University of Alabama in the USA have receivedsubstantial contributions from the pharmaceutical industry. Among those proteinsthat could be grown in microgravity to larger sizes, displaying more uniformmorphology, and yielding diffraction data to significantly higher resolutions than the

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wealth of parameters, such as convection, diffusion (thermal, solutal), radiation andreaction kinetics in three dimensions, and an excess of different species. The latter areproduced, or vanish, in chemical reactions on a very short time scales. Hence, thesesimulations have had up to now to be made with simplifying assumptions, whichoften lead to incorrect calculations because of the sensitivity of the method. Onepossibility for overcoming this problem is to neglect one of the main parameters,namely convection.

If convective effects can be neglected, the simulation of single-fuel-droplet combustioncan be treated as a one-dimensional problem instead of a three-dimensional one, andthe simulation of droplet array combustion will be reduced from three dimensions totwo. Therefore, data from convection-free experiments conducted in a microgravityenvironment can be used for the validation of the basic simulation model. This will bean important step in validating the whole process simulation model.

Fuel-droplet research has shown the existence of multi-step ignition, which influencesthe mean ignition delay time. Based on this, new binary models have been developedthat allow much more exact simulation of the behaviour of technical fuels (e.g.decane/trimethylenebenzole for kerosene). Numerical simulation of microgravitydroplet-ignition experiments showed the large differences between the simplified models,based on reaction kinetics in a homogeneous gas phase, and the real behaviour.

Microgravity combustion research therefore involves both fundamental research andapplied basic research. Without the stimulus of and the volume of data gathered frommicrogravity experiments, the improvement of simulations of industrial combustionprocesses would not be feasible.

- Ceramic and Metallic Powders

Advanced ceramic materials constitute an emerging technology with a very broadbase of current and potential applications and an ever-growing list of materialcompositions. Advanced ceramics are inorganic, non-metallic materials with differentcombinations of fine-scale microstructures, purities, complex compositions andcrystal structures, together with accurately controlled additives. Such materialsrequire a level of processing science and engineering far beyond that used in makingconventional ceramics. This new generation of high-performance materials holds thepromise of a total market worth billions of dollars. Collectively, they represent anenabling technology, the development of which is critical to advances in a host of high-technology applications, ranging from modern microelectronics to future car enginesand superconductors.

The outstanding properties possessed by advanced ceramics are achieved throughspecial compositions and microstructures that require very careful control throughout


a low voltage X-ray facility onboard the Space Station is being considered. This wouldgreatly facilitate the transfer of results to the ground, because the delicate transport ofthe newly-grown tiny crystals would be avoided.

- Combustion Research

For as long as spaceflight technology has existed, it has been necessary, due to safetyrequirements, to investigate how fires would start and flames would spread in gaseousmixtures (diffusion and premixed flames), in insulation (smouldering combustion) or inflammable liquids (flammability limits, evaporation rates), under microgravityconditions. The results have shown that combustion processes under those conditionsdiffer from those in normal 1g conditions. Furthermore, the reaction products of thecombustion process must be known. These are highly toxic in some cases and, moreremarkably, are different if produced in a space or in a 1g environment. Due to thesedifferences, alternative methods of fire detection and fire fighting have to be developedfor and used in space.

The reason for the different behaviours is the presence of buoyancy convection onEarth. Under 1g conditions, convection is the determining transport process incombustion – much more so than diffusion and radiation. In a microgravityenvironment, where free convection is nearly zero, the heat and mass transport isdetermined mainly by diffusional transport, the magnitude of which is comparativelysmall. Therefore radiation, which is not directly affected by gravity, starts to play amore important role. Because of these differences for the three transport parameters,combustion in space is weaker and the diffusion rate and the material consumptionare lower than in normal terrestrial combustion.

Combustion research under microgravity conditions has contributed significantly toour understanding of its basic characteristics. However, priority is not given to thepossible applications of those combustion processes. Rather it is seen as anopportunity to acquire knowledge about the influence of gravity on the differenttransport parameters.

The examples described in Section 2.3.7 have shown how detailed investigationsunder microgravity can be applied to improve numerical models and also to gathermore precise data to be implemented in the models. These models have beendeveloped in order to increase the efficiency of technical combustion processesapplied in transport and energy technologies. Major R&D objectives are reductions infuel consumption and a decrease in carbon dioxide in exhausts and in atmosphericpollution. These developments go hand-in-hand with attempts to use fuel with lowsulphur contents.

The development of three-dimensional simulation tools has to take into account a

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Many biotechnological processes need to be carried out using immobilisation of thebiocatalysts. Encapsulation is considered a powerful method of immobilisation. Thereare many examples of applications of this technique in various fields:

– Plant cell cultures allow the production of different metabolites used for medical,pharmacological and cosmetic purposes. Cell immobilisation improves the efficiencyof the cultures by imitating the cell’s natural environment.

– Immobilisation seems to be the technique of choice in many industrial processes infood, and especially in beverage, production. Beer, wine, vinegar and some otherproduction processes have traditionally used immobilisation procedures withadhesion culturing (e.g. acetobacter in vinegar production) and in the modernapproach, with entrapment of yeast biomass (e.g. sparkling wines).

– Continuous fermentation produces a higher overall performance than batchfermentation. To avoid wash-out of the biological catalyst from the reactor, it isnecessary to immobilise it. This principle is applied in ethanol and solvent production,sugar conversion and waste-water treatment.

– Implantation of endocrine cells is one of the most promising treatments for diseasessuch as diabetes. However, without the protection provided by a microcapsulemembrane, cells would be rejected in just a few days.

– In pharmaceutical treatments, a single application of a drug would ensure a veryefficient procedure. This could only be realised with a microencapsulated drug.

It therefore appears that micro-encapsulation has strong potential in thebiotechnology and biomedical fields (it may even be extended to ‘non-biological’systems).

Though the actual market for microcapsules in biotechnology and medicine is stilllimited, one might expect a very large growth in encapsulation technologies in thecoming decades. To give an idea, the treatment of diabetes with encapsulatedpancreatic islets represents a real solution for 7 million sufferers in the USA, and hencea potential cash flow of US$ 2.5 billion per year. Many small companies have beencreated in North America in the two last decades, with impressive capital investments(often more than US$ 30 million), to develop micro-encapsulation methods. Similarprogress has been made in Japan.

It is therefore important that European industries develop similar backgroundexpertise in order to be able to compete with Japan and the USA. In the past, mostresearch has been directed towards improving processes through an empiricalapproach by trial and error. Our fundamental understanding of microcapsuleformation is therefore still limited.

One of the main limitations in the study of microcapsule formation is that, undergravity, droplets or particles must be subjected to movement during the encapsulation


the successive stages of processing: powder synthesis, powder sizing, rheology control,consolidation and forming processes, sintering, final machining and inspection.

For most advanced ceramic components, the starting powder is a crucial factor,because their performance characteristics are greatly influenced by the precursorpowder’s characteristics. Among the most important are the powder’s chemicalpurity, particle size distribution and the manner in which the powders are packedbefore sintering. Powders with a narrow size distribution can be compacted intoordered arrays and, when in the submicron region, these powders are sintered atreduced temperatures. Consequently, in the processing of advanced ceramics, there isa growing need to develop synthetic techniques capable of producing submicron,chemically pure powders with a narrow size distribution. However, cost is again afactor, since the new synthetic processing techniques are comparatively moreexpensive than today’s manufacturing methods.

Current research concentrates on the vapour-phase synthesis of fine powders and thinfilms, with a special focus on nanoparticles and on nanocrystalline powders. Theprocesses of interest include vapour condensation, gas-phase chemical reaction, flamesynthesis, plasma reactions, aerosol decomposition, spray pyrolysis and chemical-vapour deposition. The role of nanoparticle formation and growth on the surfacesduring thin-film growth is a rapidly growing topic. Basic aspects of interest includeparticle formation, growth and crystallisation. Practical aspects are also important,including gas-flow profiles and temperature distributions, powder-deposition control,reactor design and powder collection. Other important practical issues include reactormodelling with combined CFD-aerosol modelling tools, as well as the in-situ and ex-situ characterisation of particles for process optimisation and control. Synthesis ofnanocrystalline particles and films for various applications including pigments,ceramics and electroceramics, conductive agglutinants, catalysts, advancedpharmaceuticals and nanoelectronic devices such as single-electron transistors, are alltopics of ongoing research.

It is evident that microgravity can be used as an efficient tool for applied research inthis area. The simple reason is that gravity causes sedimentation of the particles andnatural convection accelerates agglomeration. To study details of the reactionprocesses, in particular to observe critical mechanisms under slow-motion conditions,the use of microgravity is absolutely essential.

- Micro-encapsulation

Many biological systems in their natural state are immobilised. For example, withoutretention, cells would be washed away by flowing water. Therefore, most functions ofliving systems are based on the confinement of reactions within a limited space. Themembrane also provides the protection for the internal material.

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A better knowledge of the metabolic control of the growth and differentiation cantherefore be achieved from experiments with the culturing of animal cells and tissuesin space. This can lead to improved artificial organs and bioreactors.

Most of the experiments have been performed on Earth since the beginning of the1990s under ‘simulated’ microgravityconditions, using the rotating-wallculture vessel developed by NASA.Various tissues, such as animal heartcells, bovine cartilage cells or tumourcells, were used. However, this system isnot well adapted to the cultivation ofcomplex tissues; it is more suited to thegrowth of spheroids or cell clumps foruse in cancer research.

A well-documented space experiment oncartilaginous constructs, flown duringShuttle/Mir missions, has shown thatthe space samples were smaller, morespherical and mechanically weaker thantheir terrestrial equivalents. Thesefindings have been attributed to theabsence of gravitation-induced effects inspace on the growth and development ofthe engineered tissue.

3.3.3 Industry’s Attitude to Research in Space

Industrial research generally aims at the development of new or improved processesor products that have to be brought to market in a timely fashion. In order to becompetitive, industry will only invest in research and development if it foresees ademand from customers who would be interested in buying these products. Theutilisation of space within relevant research and innovation efforts can be expected ifbenefits can be identified which would counterbalance the required investment.

The research that industry believes is needed to overcome the technology barriers inmanufacturing and process technologies generally falls in the following areas: – fundamental understanding – design aids – processing technologies – sensors for in-situ monitoring and control.


process to avoid sedimentation and coalescence. Droplet speeds may reach severalmetres per second, and it is then quite difficult to observe the microcapsules duringtheir formation. Process analysis is therefore mainly based on the final microcapsulecharacteristics. The initial stage of capsule formation in particular is very difficult toobserve. Mixing of the particles leads to high convection, and the processes at thedroplet interface are then speeded up and considerably modified by this effect. Highconvection movement may even occur inside the droplet itself. Microgravityobservations will allow greater flexibility to study the effects of the differentparameters that control microcapsule formation.

A recently established Topical Team, supported by ESA, has been tasked to acquire thenecessary knowledge about industrial needs in this area and, in collaboration withindustrial partners, to develop new or improved processes using microgravity as oneof the key tools. The intention is to give European industry a leading role in the micro-encapsulation field.

- Tissue Engineering

The business of creating spare parts for the human body is becoming ever morerefined. Scientists are now engineering living human tissue in the laboratory, whichmay one day be used to replace human organs such as the liver and kidneys, as wellas bone, cartilage or skin.

About 18 000 human organs are transplanted annually in the USA, while an estimated100 000 Americans die whilst waiting for a spare heart, liver, kidney, or other organ.Ultimately, the commercial availability of laboratory-grown tissues may make theexpensive organ harvesting needed for traditional transplantation and reconstructivesurgery obsolete. The overall market for engineered tissues has been estimated to bein the US$ 400 billion range, of which US$ 80 billion is estimated to be the value of theengineered tissues themselves.

Many experimental data, obtained in micro- to hyper-gravity conditions or inmicrogravity simulation studies, indicate a change in cell function that is related to thegravity level. Subtle modifications in the mechanical and biochemical micro-environment trigger changes in cell-cell relations or in the cell function withindifferentiating tissue (see Sections 2.2.1/2).

Investigation of these minute changes will benefit from the increased stability of fluidsystems in space bio-cultivators and from the reduced mechanical loading undermicrogravity conditions. It will be particularly important for an improvedunderstanding and definition of the environmental factors needed to mimic organo-typical culture conditions.

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Figure 3.3.2. ESA’s Space Bioreactor forsuspension culturing of sensitive cell and multi-cellular systems

– The experimentation cost is too high. This is true for the flight iself and also for theconstruction of facilities and the efforts necessary for experiment preparation. Theannouncement policies and selection procedures of the various agencies are seen asprohibitively slow and inflexible by the private sector. Consequently, they prefer tospend their money on the terrestrial research alternatives.

The outcome of discussions with representatives from the private sector showed, atfirst glance, that the kind of research that had been identified as benefitting from theinclusion of microgravity was, in the majority of cases, considered useful. On the otherhand, the areas and topics identified were characterised mostly as basic research.They did not reflect the possible contribution of microgravity to the solution of aparticular industrial research problem.

This means that the usefulness of microgravity as a new tool for research is generallynot questioned. However, a great number of the problems that could be solved usingmicrogravity would belong mainly to the category of fundamental or application-oriented research. In industry’s opinion, this kind of research should be carried out byacademic researchers using publicly funded research budgets. To attract industry,applied-research tasks need to be based strictly upon the requirements of theindustrial-product-driven research and development. In addition, there needs to be ahighly visible calculable benefit from the possible results for the improvement of amarketable product. This has appeared to be lacking in many of the projects orproposals identified.

Most of the industry researchers contacted explained that this attitude reflects achange in the companies’ research strategies compared to the situation even just afew years ago. Research managers of large companies active in the automotive andengineering sectors, for example, could not even be motivated to discuss the topicwith their scientists. This was because the research possibilities offered by theinclusion of microgravity were considered too basic to warrant near-termconsideration. They also explained that, for economic and commercial reasons, thekind of application-oriented research that was the subject of past EC-funded projects,and was carried out with their participation, is no longer actively pursued within thestrategic aims of their companies. The main reason is that those tasks were often onlyindirectly related to the development of a marketable product.

Consequently, a number of the industrial research activities previously performed incollaboration with scientists from universities have been terminated by industry andare no longer considered future topics for industrial applied research. It is expectedthat henceforth this kind of research will only be carried out by universities andresearch institutes, and that direct industry involvement will only occur if potentialprofits from that direct investment are clearly visible.


A critical area of research that will rely heavily on public funding is the developmentof a better fundamental understanding of processes like solidification, chemicalprocessing, energy production and transformation and biotechnological production(cell factory, tissue engineering). These are processes in which the influence ofconvection can play a role, but one that often cannot be quantified. Research canprovide the information to enable engineers to improve the design and productivity ofindustrial products. This is increasingly being achieved by numerical simulation, forwhich better models and more precise input data are needed. In certain areas, thismight be achieved by the utilisation of space. Successful research in these areas wouldhelp industry make progress towards three goals:– improved productivity– reduced time-to-market, and – reduced energy consumption.

To identify the industrial interest in using the International Space Station for thosepurposes, a number of representatives from industry were recently asked, in differentstudies executed on behalf of ESA, if they would be interested in considering it as a sitefor targeted applied research and, if so, under what conditions. Although the majorityof the answers were rather disappointing with respect to possible near-terminvestment, it was accepted by a number of the industrial scientists that someparticipation in projects dealing with research in the microgravity environment couldbe of advantage. Even so, they had almost no concrete ideas about the purposes forwhich such research could be applied in product research and development. Thegeneral opinion was that using the weightlessness of space would be the subject ofbasic research, the results of which might lead to a better understanding of thephysical phenomena that take place in processes involving molten metals, multi-phase fluids (consisting of liquids, gases and particles), or the interaction andaggregation of cells and bio-molecules.

The major reasons why industry, at present, tends to eschew the opportunities thatcould arise from the utilisation of space for applied research and development stemfrom three areas of concern:

– Because research under microgravity is a new discipline and, particularly, becausethe experiment opportunities have been so scarce compared to those of ground-based research, the results achieved so far are few and often rather basic. Thevisibility of the industrial potential and the possibilities for direct commercialapplications still remain to be elaborated through suitable promotional means.

– The access conditions for industry-related research in space are presently in conflictwith some of the requirements of a straightforward approach directed towards theinclusion of microgravity in on-going (terrestrial) application-oriented researchprogrammes and projects.

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innovative purposes, in order to increase and strengthen its competitiveness. Theseactivities are mostly related to the transfer of available results and ideas from previousfundamental experiments into more application-oriented and industry-driven researchefforts.

The Microgravity Application Promotion (MAP) Programme is directed at preparationsfor the utilisation of the ISS. Almost ten years ago, ESA launched a programme toinvolve industry in applied research on the Space Station. Rather like the NASA‘Centers for the Commercial Development of Space’ (CCDS) programme, an approachwas initiated in which groups of scientists would team up with industry. The objectivewas to identify those areas in which the utilisation of space could be one importantelement in the research and development of an industrial programme. Originallycalled RADIUS (Research Associations for the Development of the Industrial Utilisationof Space) programme, it was later supplemented by broadening the approach throughthe establishment of Topical Teams (TT). In these Teams, new space-environmentapplications were discussed in a series of workshops with industrial participation.Covering the different fields and disciplines of materials science, fluid sciences andbiotechnology, these workshops proved to be an important step in identifying applied-research problems that could usefully be solved by using microgravity as one of thekey tools.

To get the MAP Programme started, an Announcement of Opportunity (AO) was issuedin 1998. It asked for proposals in which researchers and research teams, with partnersfrom industry, suggested ideas and new approaches to include the utilisation ofmicrogravity in their overall product-oriented and market-driven applied-researchactivities. Out of the 150 proposals submitted and evaluated by a peer-review process,about 50 were ranked as ‘recommended’. Many of them were ranked as ‘highlyrecommended’, or even ‘outstanding’, in terms of their scientific quality and potentialfor solving significant industrial-research questions. It could be clearly shown that,contrary to frequently heard statements, the proposals presented represented a set ofinitial nuclei, needed to prepare and to promote the desired industrial involvement inthe utilisation of the ISS in the long term. Details of currently accepted proposals areto be found in the Tables in the Appendix (Chapter 6.8).

To illustrate the industrial potential of the MAP approach, several of the recentlyselected project proposals are described below, which fall into the following industrialresearch sectors:– advanced casting technologies– crystal growth of semiconductor and sensor materials– industrial combustion– multiphase fluids in chemical processing– biotechnology– medical applications and health care.


The conclusion is that to involve industry in gravity-related research and ensure itsparticipation in the utilisation of microgravity in the long-term, the specific researchneeds of the individual companies have to be addressed. The development of productsand processes has to be analysed in much more detail than was possible hitherto, andthese needs and requirements have to be taken as the basis for future projects.

3.3.4 The ESA Microgravity Application Promotion (MAP) Approach

It is realistic to assume that benefits from using the International Space Station couldbe the harvesting of results or data that:– are not otherwise available from research on Earth– would speed up the innovation process and the time to the market– could put the enterprise in a unique position to sell its products.

The results of this research can be considered as a kind of ‘added value’, which wouldjustify the investment of going into space. Areas to be addressed are:– on-going industrial research where gravity-influenced phenomena could be relevant– industrially relevant research problems or questions– the use of microgravity as a tool to solve those questions– quantification of the ‘added value’ of microgravity’s contribution– non-space funding programmes (e.g. European Commission)– possibilities for industrial sponsorship.

From the experience gained so far, it appears that the possibilities offered by the ISSfor industrial research will be limited, but some of the fields for its utilisation canalready be clearly identified. To do this, it is necessary to study the needs of industrialresearch carefully and to identify areas where the utilisation of the space environmentas a tool could bring further advantages. It is also apparent that suitable methodshave to be developed for including the expected results in the industrial process andproduct development. It has also been shown that for industry to consider using thespace environment in such an innovation process, a certain promotional approach isneeded to overcome the obstacles that have so far have limited its involvement.

The industrial research possibilities can be categorised into:– processes improved by data and knowledge from space (e.g. numerical simulation)– products developed from new ideas generated from space results– shortening time to market through space-research contributions– saving on development costs by use of space– products processed in space and sold on Earth.

Several approaches have been started to promote the industrial utilisation potential ofthe International Space Station. The aim was to initiate suitable efforts to encourageEuropean industry to use the space environment and the related infrastructure for

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which are aimed at improving the physical models that are the underlying basis forthe numerical simulation of advanced casting technologies. The research workcomplements that in the ‘determination of thermophysical properties’ project. It wasindustry itself that clearly voiced the need for improvement of the presently usedphysical models, particularly for the transition stage of cooling between liquid andsolid (mushy zone). In this range, the competition between the growth of columnarand equiaxed grains is not well-understood, and therefore these phenomena will beinvestigated by comparing the heat and mass flows in the presence and absence ofconvection. This will lead to a more quantitative understanding of the basic physicalprinciples that govern the formation of microstructures in modern solidificationtechnologies.

The knowledge gained from this research is expected to contribute significantly toimprovement of the integrated modelling of the grain structure in technicallyimportant castings, based on the demands from the industrial partners in the project.The main emphasis will be on frequently used Al- and Cu-alloys, supported byfundamental investigations of transparent model systems. A primary goal is toimprove the so-called CAFE (Cellular Automaton Finite Element) 3D model, developedand applied by several of the industrial research partners to predict the dendritic grainstructure of directionally solidified parts or components.

The second project has the objective of identifying the interaction of magnetic fieldsand fluid flow in continuous casting. This process is used to fabricate long material forfurther hot and cold working to sheets, bars and wires. Industry has been usingmagnetic fields to brake and to control the liquid-metal flow for more than twodecades, but the models applied for numerical simulation are already at theirtechnical and physical limits in terms of validity. To enable more economic processingand to improve the processing speed used in casting slabs and billets to a fewmetres/second, it is necessary to understand the complex interactions in the meltbetter. This in turn will lead to the desired quality improvement in the numericalsimulation and to further optimisation of the continuous casting of steel andaluminium alloys.

- Crystal Growth of CdTe and Related Compounds

Semiconductors like cadmium telluride (CdTe), and related compounds such as(Cd,Zn)Te, are required as highly perfect single-crystal materials for advancedapplications in X-ray detectors and photo-refractive devices (e.g. ultrasonic sensors),and as substrate material for infrared detectors and electro-optical devices. However,the quality of those materials produced with current single-crystal-growth processtechniques does not match the level required for the applications envisaged. Inaddition, the low production yields have made use these expensive materialsunattractive from an economic viewpoint also.


3.3.5. Selected MAP Projects

Presently some 48 projects have been approved by ESA, most of which were startedduring 2000. Mainly ground-based research will be financed for the first two years,during which the industrial questions for future microgravity research to addressshould be identified. Thereafter, precursor experiments are planned in selectedresearch areas using either early opportunities on the ISS, or Spacehab and sounding-rocket missions.

The following are some of the most advanced project topics:

- High-Precision Thermophysical Data for Liquid Metals

This project is based on the fact that the accuracy of measurement of thermo-physicaldata for metallic melts is limited with the methods usually applied in ground-basedlaboratories, as discussed above in Section 3.3.2 and earlier in Section 2.3.3. It hasbeen shown that by using advanced methods such as the containerless processing ofreactive melts of high-temperature materials (iron, nickel, titanium alloys), the melts’reaction with the crucible materials can be avoided. This can lead to more accuratevalues for the properties to be determined. This precision can even be further increasedif convection effects can be suppressed under microgravity conditions. It is thereforeexpected that the outcome of the research will benefit the numerical simulation ofliquid-metal forming processes, such as casting, welding and metal spraying.

In contrast to earlier microgravity research in the field, which already provided proofof concept, the ongoing project is concentrating on alloys of technological andcommercial interest. The industrial partners are the market leaders in the applicationof numerical simulation, representing materials producers and end users, softwarecode developers and producers of measurement equipment. It is expected that thebenefits resulting from the project will improve the predictability of casting processes(investment casting, directional and single-crystal solidification, continuous casting),leading to micro-structural improvements and improved quality and reliability of thecast components and parts. Examples are turbine blades for static and aircraft gasturbine engines, bone replacement parts made from titanium, and cast aluminiumand magnesium casings for mass-produced products such as laptop computers andmobile phones.

- Microstructure Formation in the Casting of Technical Alloys

There are two projects in this domain:– Columnar-Equiaxed Transition in Solidification Processing, and– Control of Convection by Magnetic Fields

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Experience is still important, but costs and competition require an increasingly rapidinnovation process, with as little experimentation as possible. The simplifiednumerical simulation models are, however, only as good as the respective basicknowledge. The understanding of these basic relations is, as explained above, mostlyachieved by microgravity-based research activities (see Section 2.3.7).

In addition, data on material properties applied in simulation processes are of greatimportance in order to check the correspondence between simulation results and theactual behaviour. Since material data contain no gravity-related parameters,microgravity laboratory is the only way to obtain these data accurately, without anymasking or distorting external influences (normally of convective, but also of asystematic-industrial nature). These data affected by external influences may cause,by an accumulation of mistakes, considerable deviations between the simulation andthe real behaviour.

The objectives of two related projects are directed towards improvement of thenumerical simulation tools and codes that are presently under development byindustry. Efforts are also directed towards studying the influence of water sprays onthe processes, with the goal of using the acquired knowledge also in fire-fightingapplications. Major developments are the design and construction of new laserdiagnostic systems allowing one to study details of the experimental investigations inspace and on Earth.

- Bioreactor in Space

ESA has recently recognised the need for a 3D bioreactor in space, in order to studytissue function and reaction to gravitational stress. A Tissue Engineering project hasjust started, with the selection of research topics and the development of theappropriate instrumentation. One of the aims is to develop a BiotechnologyMammalian Tissue Culture Facility (BMTC), which is presently being considered for useon the International Space Station.

The utilisation of ‘bionic’ organ models in tissue culturing will allow the elucidation ofthe role of weightlessness on (human) cell and organ function in space. Benefits fromtissue-engineering experiments in space, for use in terrestrial industrial applications,are expected to come from the following areas:

– Improved knowledge will be gained of the 3D growth of organ tissues. The reducedshear stress or tissue pressure will help in the precise regulation of the micro-environmental conditions necessary to establish and maintain polarity in tissues,with the potential for future development of artificial organs.

– New organo-typical culture models, replacing animals, will help in monitoring thehealth of humans in space (astronauts) and will allow the prediction of health risks.


The project aims to develop new growthtechniques, based upon the experiencegathered with space experiments. It wasshown that the containerless growthmethods tested in space provided single-crystal material of unprecedentedquality and yield. The reason for the improvement is the strongly reduced level ofstress on the material due to the lack of direct contact with the container walls. Theaim is to transfer those benefits to processing on Earth, through the development of‘quasi-containerless’ processes in which the grown material is in contact with thesupporting crucible or ampoule at a few points only. This will be achieved by thedevelopment of advanced growth techniques using proper geometric wall design andnon-wetting conditions in the melt.

Eleven European companies with different commercial interests are participating inthe project. Their aims are to develop and to apply new material testing methods, totest the performance of the grown materials for the envisaged applications, and tofabricate model devices allowing them to estimate the economic potential of thematerials in X-ray detectors for medical and non-destructive testing, or in the electro-optical switches used in modern communication technologies.

- Technical Combustion Processes

It is becoming clear that society needs to reduce the rate of consumption of fossil fuelsin order to contain the threat posed by atmospheric pollution and the accompanying‘greenhouse’ effect. That leads to the need to improve the efficiency of power andenergy production and conversion processes in both transport and power-planttechnologies. These requirements have not only triggered the development of new andlighter materials, but have also initiated efforts to reduce fuel consumption through abetter understanding of the physico-chemical processes needed for the developmentof more effective combustion systems.

Though gravity appears to be insignificant in the case of technical combustionprocesses, which are mostly turbulent, combustion data from microgravity researchcan still contribute to further improving efficiency. The reason is that the developmentof technical combustion systems is today based more than ever on simulations.

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Figure 3.3.3. A space-grown cadmium-telluride crystal, suitable for high-sensitivity X-ray detectors. The limited sizeof Earth-grown crystals has held back theirapplication

Industrial participants in the project include suppliers of biomedical instrumentationand pharmaceutical companies.

3.3.6 Industry-Oriented Space Research and the European Commission

The scope of the research proposed in the MAP projects is limited to use of themicrogravity environment as a tool for achieving ‘added value’ in the approach tosolving industrial research problems. Since the Agency’s funding possibilities arelimited, it would be desirable to get additional financial support from non-spacesources, such as the 5th Framework Programme (FP) of the European Commission (EC).Previous experience showed that co-funded projects, in which the cost of ground-based research is funded jointly by industry and public research programmes, leadsboth to a reduction in ESA’s costs and a substantial increase in the usefulness of theresults for the development of industrial processes or products.

Most MAP projects are eligible for additional funding from the European Commission(EC), provided their objectives coincide with the research topics and time frames (callsfor submissions in different programme areas) of the EC’s ‘Growth’ and ‘Life’programmes.

It is generally expected that, at least at the beginning of the Space Station utilisationphase, most of the experiments will be based on the existence of such joint projectsbetween industry and applied-research institutes. The research will mostly be pre-competitive in nature, falling within the typical conditions associated with theCommission’s Framework Programmes. Because these conditions require asubstantial contribution from industry (generally 50%) and a market-orientedresearch exploitation plan, such projects can be considered as a model for the futureindustrial utilisation of space.

The concept of ‘virtual institutes’ within the EC’s Framework Programme is based onthe grouping of projects with similar industrial research objectives. It would allow jointESA- and EC-funded industrial research efforts in selected application fields. It wouldalso allow the streamlining of related research objectives, through the distribution oftasks and an intensive exchange of information and results. This would allow theharmonisation of applied research in the pre-competitive stage.

The project selection would include:– themes of outstanding/highly-recommended MAP projects– incorporation of space-based experiments into the overall research activities– use of the results for the improvement of industrial processes and products.

Another important aspect is that EC funds could be used for space-related activities,which has not been possible so far at a programmatic level.


– New in-vitro models for use in drug screening and for the development of artificialorgans will be developed for space-physiology studies, which will also be of interestfor terrestrial use.

– Better understanding of the influence of mechanics and weightlessness on intracellularinteractions may lead to the discovery of new modes of drug action and newcompounds. This can be applied in the development of new molecular targets/drugs for the pharmaceutical industry.

The development of innovative technologies (microsystems, optical diagnostics), leadingto improved bioreactor technology for organ tissue culture, will result from constraints likelimited volume and power, and possibly find application in commercial markets.

- Osteoporosis and Bone Remodelling

The topic of this project was one of those themes that were selected in the early phaseof promoting the industrial utilisation of space and, in particular, the application ofmicrogravity for human health issues. The observation that a loss of bone mass occursin astronauts and animals under long-duration weightless conditions has led to theidea to study this effect in a more quantitative manner. Furthermore, it has beensuggested to use the results achieved in space not only to develop methods forcountermeasures during human space travel, but also to transfer the knowledge tosolve the Earth-related problems of osteoporosis, which has developed into a diseaseof major concern for elderly people.

In Europe, there are more than one million osteoporotic-related fractures each year.The costs of associated treatments are a significant factor of interest for thepharmaceutical and biomedical industries. It is therefore not surprising that theprivate sector is interested in the results of studies conducted in space, which could beused to simulate bone loss under strongly accelerated conditions. The testing ofpossible treatments and countermeasures could also be performed on the ISS, thusallowing significantly quicker proof of their efficiency.

Given these considerations, the ESA-sponsored Osteoporosis Project is based onseveral application-oriented and industry-driven objectives:

– quantitative study of bone loss during spaceflight and transfer of the results into aphysiological model by in-vivo observation and in-vitro samples, to be used also fordrug screening

– investigation of the influence of gravity/microgravity on bone cell cultures– development of a high-resolution instrument for the quantitative characterisation of

bone density and bone architecture– testing of the efficiency of pharmaceuticals and specific exercises for the prevention

or deceleration of osteoporosis.

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ESA’s approach to promoting future involvement of the private sector in the use of theISS is the MAP programme, which focuses on two major themes. The first is thedefinition and preparation of experiments within previously selected networks havingindustrial participants. The second involves the so-called ‘ESA Topical Teams’, co-ordinated by experienced scientists coming from basic research. They have the taskof using the developing knowledge on gravity-related phenomena to identify and solveindustry-related research questions. Based on these existing activities, the promotionprogramme is able to fulfil the industrial users’ demands by providing information,establishing a dialogue with industry and making available attractive researchconditions.

Industry is generally not aware of the kinds of benefits that it can obtain from theutilisation of the ISS. Moreover, the results of previous microgravity missions are noteasily available to ‘outsiders’. Because flight opportunities have tended to be rare andthe most significant results have generally been published at space-relatedconferences, information about experiment results and their possible benefits forindustry tends to be fragmented. Experience has shown that industrial scientistswould not develop their own research proposal merely as a result of seeing brochuresand learned publications.

One major aspect of the information approach must be participation by industry inthe setting up of Europe-wide teams and networks involving researchers from bothacademia and industry. Since it is expected that applied research on the ISS will starton pre-competitive projects, industrial researchers will be motivated to work jointly onthe identification of industrially relevant questions for which the ISS and itsenvironment can be used as a ‘tool for research’. A further objective is to initiateindustrial projects in which ground-based research would be supported by the EC’sFramework Programme. In that event, ESA would finance the space-related ground-based activities and the flight opportunities, along with the participation ofresearchers from universities. Only in the long term would industry be asked tocontribute to the space-related costs, provided a clear return-on-investment for themcan be identified.

This new approach is aimed at generating continuous demand for industrial researchon the ISS in the medium and long term. This will be achieved by initiating ground-based industry/institute networks on selected research topics. The idea is that thosenetworks, or ‘Virtual Institutes’, should cover a broader range of related projects,based on industrial research demand. They would perform co-operative research,combining the originally separate scientific and applied research goals. It isanticipated that once such networks have been established, further interest fromindustry will be created as a consequence of the quality of the data and resultsreceived from space.


Industrial research will either be conducted in multi-user facilities developed primarilyfor more fundamental research, or in dedicated experiment facilities provided by theusers themselves or by contracting space-experienced companies. Users coming fromindustry and bringing their own payloads to the Space Station may well not befamiliar with ISS operating procedures and safety considerations. Accessarrangements tailored to the specific needs of individual industrial users, including theconfidentiality and proprietary rights issues, will therefore need to be developed.These issues will be handled on an individual user basis by the ISS operator.

3.3.7 Conclusions and Outlook

Non-space industry’s interest in using the ISS for applied research is expected to centremainly around taking advantage of its weightless environment. The results of theircombined space- and Earth-based research efforts can then be used to improve theirexisting processes and/or products, thereby gaining them a competitive advantage.In some cases, specially formed small companies (spin-offs from institutes oruniversities, funded by venture capital) will conduct the space-based research undercontract to industry and with partial support from public funding programmes.

Given the nature of the space experiments carried out in the past, industrial demandfor using the ISS for applied research is expected to come primarily from the followingareas:– materials processing and fabrication– optimisation of process technologies– increasing of efficiency in energy conversion– data for numerical simulation needed by code developers and users– development of new biotechnology processes– design and testing of new pharmaceuticals.

More results from space experiments need to become available to stimulatesignificant involvement by industry in the International Space Station. Greaterindustrial participation in ISS utilisation for commercial benefit will therefore dependon the establishment of a promotion programme geared to convincing industry of thepotential benefits. The industrial possibilities mainly rely on using the microgravityenvironment as an application-oriented research tool to gather more accurate data on,or a much improved understanding of specific physical and biological phenomena,leading to benefits for industrial, environmental or medical applications.

In addition, study and validation of the behaviours of certain process steps undermicrogravity may be of interest. This would ensure that such technologies could beused to generate additional business from the exploitation of Earth-boundtechnologies in space applications (e.g fluid loops, heat exchangers, etc).

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Major elements of this approach are to:– establish industry/academia research networks– initiate research networks with combined ground and space research– apply for funding from industry and non-space funding programmes– generate continuous demand for industrial research on the ISS in the medium and

long term.

The experiments on the ISS will be designed to solve key research questions andacquire data and knowledge not available from research on Earth. This approach ofincluding space results to achieve ‘added value’ for solving industrial problems wouldbe based on a business plan in which the expected risk must be taken into account,and from which the potential return-on-investment could be calculated.

Because of the different uses envisaged for the ISS as a site for non-R&D relatedpurposes, it is suggested that applied research be combined also with activities thattend to fall into the public-relations category. Many companies use symbols andpictures from space to demonstrate progress and competence in high technology. Onthe other hand, TV broadcasts on advanced research tend to have high viewing ratingswithin the educated public. TV transmissions from the ISS could therefore be used bycompanies to improve their image and to relate their product to ongoing research andthe facilities in which the research is being conducted. Other similar opportunitiesinclude using space research and demonstrations, including astronauts, as a basis forquestions and answers related to the research being performed aboard the ISS. Suchan approach would have the added advantage of helping to create/preserve a positiveimage of the ISS, thereby enhancing industrial interest for its future use for appliedresearch.

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CHAPTER 4 THE GROWTH OF MICROGRAVITY RESEARCH

– From Skylab to the International Space Station

G. Seibert

4.1 The Origins of Microgravity Research in Space

4.1.1 Early US and Soviet Activities

During the 1970s, only the USA and the Soviet Union had access to the microgravityenvironment that exists in a freely drifting spacecraft or an orbiting satellite. Therewas no European manned spaceflight or satellite programme that includedmicrogravity experimentation at that time.

- The Skylab Programme

The objective of the Apollo Programme, to land an American astronaut on the surfaceof the Moon before 1970, was achieved in July 1969. Five further successful Moonlandings, extending through to 1972, followed.

The Apollo capsule had been constructed to accommodate three astronauts duringtheir flight to the Moon. It was not designed as a laboratory for microgravity studiesin the life and materials sciences. Consequently, there was insufficient space toaccommodate sophisticated research equipment. Nevertheless, the first exploratoryspace microgravity experiments were performed on these missions, including low-temperature composite casting, some simple fluid-physics experiments andelectrophoresis experiments.

By 1972, after six Moon landing missions and the return of almost 400 kg of Moonrocks and soil to Earth, American public interest in further Moon missions waswaning. There were other national concerns. NASA decided to cancel the three furtherApollo lunar missions that had been planned. Instead, it was decided to use theSaturn-5 rocket hardware that still existed to construct a manned orbiting station that


semiconductors, immiscible-alloy processing, radioactive-tracer diffusion, micro-segregation in germanium, growth of spherical crystals, whisker-reinforcedcomposites, indium antimonide crystal and mixed III-V crystal growth, alkali-halideeutectics, silver grids melted in space, and copper-aluminium eutectics. There werealso a number of investigations in biology (bacillus subtilis, human lung cells),biotechnology, human physiology and medicine. Studies were also made of the effectsdue to the combined influence on living matter of the particle-radiation, vacuum, low-temperature, and microgravity environment of space.

These pioneering life- and physical-sciences microgravity experiments on Skylabattracted worldwide interest in many research fields. They led to the start of dedicatedmicrogravity materials-processing and of space life-sciences research programmes inthe USA. It became obvious that research in microgravity would lead to advances inthe fundamental understanding of the properties of materials and the discovery ofnew life-sciences phenomena.

An important objective of the American, and later also of the European MicrogravityProgrammes, was to provide a sound appraisal of the probable medium- and long-term value of microgravity studies to industrial applications. However, it becameapparent that the detailed scientific information required for this appraisal would onlybe forthcoming after a series of fundamental investigations, which required thesophisticated instrumentation becoming available during the Shuttle/Spacelab era.

The reason why a full appraisal of materials processing and life sciences in space wasnot possible after the Skylab missions was the following:– The experiments on Apollo and Skylab were hastily prepared and instrumentation

such as furnaces, crystallisation chambers, and biomedical instruments, wasrudimentary compared with the experimental facilities developed later and used during the Spacelab era.

– In addition, many potential research areas in the life sciences and materialsprocessing were not explored in the Skylab programme. For example, the area ofprotein crystallisation, which became one of the most investigated research fieldsduring the later Shuttle/Spacelab period, was not addressed on Skylab.

Unfortunately, those early results from the Skylab experiments gave rise to overlyoptimistic predictions for the potential industrial benefits from space processing. TheNASA-supported studies, for example those performed by the Centre of Space Policy inCambridge (Mass.), made projections predicting extremely large benefits frommaterials processing in space factories.

Subsequently, more realistic reviews attempted to correct these predictions, by statingthat short-term economic benefits were unlikely. Instead, the scientific andtechnological problems should first be addressed so as to gain a detailed


was called ‘Skylab’. Following the termination of the Apollo Programme, thedevelopment of Skylab became the core space activity of NASA.

Skylab consisted of a third stage of the Saturn-5 rocket, modified to act as an orbitallaboratory. It had a length of 15 m, a diameter of 6.6 m, and could accommodate threeastronauts and their necessary life-support equipment. It was also able to accept anumber of microgravity research facilities for life-sciences and materials processing,together with instruments for Earth observation and astronomy.

The 99 ton orbital station Skylab was launched in May 1973, into a 400 km orbit of50 deg inclination by a 2-stage Saturn-5 rocket.

This first manned Skylab mission lasted 28 days. Just five weeks later, a second crewof three astronauts was sent to Skylab for a stay of almost 60 days. The Skylabmanned activity was concluded with a third mission launched on 16 November 1973.The three-crew members spent 84 days in space. Skylab stayed in orbit, butunoccupied, until July 1979, when a controlled re-entry occurred.

During these three manned Skylab missions, pioneering microgravity experiments inthe life- and physical sciences were performed, covering biomedical studies, thebehaviour of fluids and the solidification processes of materials. There were 21experiments in the space processing of materials. These dealt with metal melting,exothermic brazing, sphere forming, vapour growth of IV-VI compound

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Figure 4.1.1. The Skylab orbital station (courtesy of NASA)

Ten different crews visited Salyut, using the Soyuz transfer vehicle. The final visit lasted100 days. It was also visited 15 times by the cargo vehicle Progress, which carriedabout 170 different instruments. However, the Soviets did not communicate orpublish the results of these missions, which were predominantly dedicated to life- andmaterials-science research in space.

- The Mir Space Station

In February1986, the Soviet space station Mir was launched. This had an ‘unlimited’mission-duration capability and was the first true space station. It continued to circlethe Earth, at an altitude between 350 and 400 km, and with an orbital inclination of51.6 deg, until March 2001.

Mir’s configuration consisted of a core module, about 13 m long and with a maximumdiameter of some 4 m, together with five scientific modules. These were: – Kvant, a module for astrophysics, launched in 1987– Kvant-2, housing scientific and technology equipment, plus an airlock for

extravehicular activities, launched in late 1989– Kristall, launched in 1990, and dedicated to materials and biological science – Spektre, launched in 1995, and used for astronomy and atmospheric research– Priroda, launched in 1996, and dedicated to Earth observation.

The total Mir complex was T-shaped, with a length of 33 m and height of 28 m. Itsoverall mass was 70 tons.

The many visits by internationalcrews to Mir in the period from1986 through to 1999 haveprovided invaluable missionexperience in operating a spacestation and in supporting thecrew during extended stays inspace. In so doing they haveprepared the way for theoperation and the utilisation ofthe International Space Station(ISS).

In the Soviet Union, publicinformation concerning the life-and materials-science researchin space was always limited.However, it became obvious in


understanding of the fundamental aspects. These could then lead later to anapplication-oriented programme.

- The Apollo-Soyuz Test Project (ASTP)

In 1972, the Soviet Union and the USA agreed on a space mission that was intendedto demonstrate to the world that, despite the Cold War, scientific and technical co-operation should be possible. From the Soviet side, it was agreed that the man-ratedtransfer vehicle ‘Soyuz’, which since 1971 had routinely serviced the first SovietOrbital Station ‘Salyut’, would be launched and ultimately docked with an AmericanApollo command capsule. The latter was launched in July 1975 using a Saturn-1Brocket.

This ASTP mission was not only a techno-political success, which culminated inhandshakes between three American and two Russian astronauts in space on 17 July1975, but it was also a welcome opportunity to perform further microgravityexperiments in physical- and life sciences after Skylab. These were mainly follow-oninvestigations of Skylab and Apollo experiments in metallurgy, crystal growth andelectrophoretic separation of organic samples:

– four metallurgy experiments in the fields of surface-tension-induced convection,growth of LiF-NaCl eutectica, processing of monotectic (PbZn) and syntectic (AlSb)alloys, and processing of permanent-magnet materials (MnBi and others)

– three crystal-growth experiments: from the solution and from the vapour and agermanium single-crystal experiment

– two electrophoretic-separation experiments, one of which was an American ‘static zone electrophoresis’ experiment, which was tried earlier on Apollo-14; the (Anotherwas a German ‘Free-Flow Electrophoresis’ experiment. This sought to avoid thegravity-induced convection currents that disturb the separation quality of organicsamples (e.g. red blood cells, kidney cells, lymphocytes, erythrocytes).

These experiments worked quite well and they extended the database of knowledgeof research under microgravity conditions. It was, however, only a simple ‘stand-alone’mission. There was no related follow-on research opportunity to broaden the researchbase and to provide continuity of experimentation, as was desired by the scientificcommunity.

- The Soviet Salyut Orbital Station

The Soviet Union took the first step in the direction of a space station in April 1971,with the launch of the Salyut-1 orbital station. It consisted of a cylindrical module, 13 m long and 3.6 m in diameter. After Salyut-1, several further improved Salyutversions were launched, until 1982.

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Figure 4.1.2. The Mir space station

were also held on promising future research areas. The results of the early life-sciencesexperiments demonstrated that the initial hypothesis, to extrapolate from hyper-gravity through 1 g to microgravity effects, could not be sustained. Many of theexperimental results were seen to contradict the models and theories in physiologyand biology textbooks.

The Spacelab Agreement between ESA/Europe and NASA/USA specified that the firstSpacelab mission would have as its primary objectives the verification of the Spacelabsystem, the Shuttle/Spacelab interface compatibility, and the measurement of theinduced radiation environment. The secondary objective was to obtain scientific,application and technology data from the joint European/US multi-disciplinarypayload and to demonstrate, to the potential user community, the broad capability ofSpacelab for research.

The joint ESA/NASA payload required ESA to select experiments from differentdisciplines and to procure or develop the necessary hardware. This would use 50% ofthe technical resources available to the first Spacelab payload. An acceptable resourceallocation to payload elements from the different disciplines had to be found aftercompetitive experiment selection.

ESA received many proposals for experiments in the new discipline of microgravityresearch in materials/fluid sciences and life sciences. It was obvious that they wouldconstitute the major portion of the multi-disciplinary payload of the first Spacelab. Inresponse to the need to advise and guide this new research activity, in 1975 ESA setup a Life-Science Working Group and a Materials/Fluid-Science Working Group. Thelatter was subsequently renamed the Physical-Sciences Working Group. Two yearslater, the senior advisory group known as the Microgravity Advisory Committee (MAC)was established.

- The Joint US – European First Spacelab Mission

The evaluation of the requirements of the selected microgravity experiment proposalsrevealed the need not only for new multi-user research facilities, but also to perform anumber of subsequent Spacelab missions. Many of the proposed experiments were infact experimental programmes, having parameter variations as part of the study.Consequently, they needed the results of the first experiment in order to set theexperimental parameters for the follow-on experiments. This interactive andsequential experimental research process is, of course, very similar to the procedurefollowed in terrestrial laboratories.

However, the US–ESA Spacelab Agreement only provided for the first joint mission tobe free of flight costs to ESA. NASA had decided unilaterally that from the secondSpacelab mission onwards, the missions would not be joint events. They would be


the 1980s that the Soviets considered this field an important means for developingnovel or advanced materials with unique properties that they needed to makeprogress in strategic technologies. The Soviet programme was always applications-oriented. Their research was directed towards enhancing the properties of materialssuch as compound semiconductors, super-conducting alloys, magnetic alloys, lasermaterials, infrared optics, sensors, etc. It is now known that about 2000 samples havebeen processed in Soviet orbital stations, and that hundreds of kilogrammes ofsamples/specimens were returned to Earth.

In addition to these orbital missions, both NASA and the Soviet space authoritiescarried out numerous materials processing studies with drop towers, parabolicairplane flights and sounding rockets. These started long before Europe began suchshort-duration microgravity experiments in the late 1970s.

- Guidelines for Microgravity Research in the USA

The early optimism regarding the commercial possibilities of microgravity (e.g.factories in space) was dampened when, in 1978, a report by the Scientific andTechnical Aspects of Materials Processing in Space Committee (STAMPS) of the USNational Academy of Sciences was published. This concluded that the prediction ofcommercial benefits should not be exaggerated and that the scientific aspects andtechnological problems should first be addressed. Only when a detailed understandingof the fundamental aspects had been achieved could one decide on setting up anindustry-oriented research programme.

NASA followed the guidelines and recommendations of that report during the 1980s.It concentrated on the field of materials processing/fluid physics and the areas ofelectronic materials, metals and alloys, glasses and ceramics, transport phenomena,fluid dynamics and biotechnology. In life-sciences research, the field of humanphysiology and the survival and well being of astronauts in the space environment(microgravity and radiation) received the highest priority.

4.1.2 Early European Microgravity Activities

The motivation that led to the decision to develop Spacelab as Europe’s contributionto the US Shuttle Programme was described in Section 1.3, where there is also anoverview of Europe’s involvement in Spacelab missions between 1983 and 1998. Thedecision taken by ESA in 1973 to develop Spacelab caused Europe to review and takestock of the early American results of microgravity studies. The interest was to definethe future European microgravity research activities in the life and physical sciences.In order to facilitate this process, ESA organised in 1974, just after the Skylab missions,and again in 1976 after the Apollo-Soyuz Test Project (ASTP), two symposia at whichUS scientists and NASA reported on their preliminary research results. Consultations

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(conceptual design and cost estimate). These were destined to be accommodated,together with nationally planned facilities, in the Materials-Science Double Rack of thefirst Spacelab mission. ESA also studied the Vestibular Sled. These facilities had to bequalified with respect to the launch accelerations and vibration, had to meetelectromagnetic-interference requirements, and had to be compatible with Spacelab’stechnical resources, constraints and interfaces.

The studies showed that, contrary to the earlier optimistic views, the commercialinstruments used in the terrestrial laboratories could not be used for a mannedmission such as Spacelab without major modifications. They normally did not meetthe environmental constraints of the launch, had outgassing problems, were notoptimised regarding power consumption, and their thermal-control systems usuallyrelied upon convection cooling, which of course is absent in microgravity. In addition,the facility/instrument technical performance requirements of the investigations were at the edge of technological progress and often exceeded the performance of theequipment that the investigators used in their own terrestrial laboratories.

This situation led to the development of a new generation of space-qualified and high-performance experimental facilities/instruments based on an extension of existingtechnology. However, the unit costs of these new facilities by far exceeded those oftheir terrestrial counterparts. These costs were often a factor of 5 to10 higher. Thereasons for that high unit cost stem from the advanced technology that was needed,the stringent testing required for equipment to be accepted onto a manned spacevehicle, and the fact that each unit was unique.

The European and the NASA ‘Call for Experiments’ for the first Spacelab missionresulted in several hundred experiment proposals, from which 70 were selected forflight. The selection criteria were based on guidelines from the ESA/NASA Joint UserRequirements Group (JURG), which periodically reviewed the performance andresource provisions of Spacelab for the users. JURG’s guidelines for the peer selectionincluded the following for this first payload:

– ESA and NASA experiments should be complementary– the payload should be open to science, applications and technology experiments– the experiments should take advantage of Spacelab’s unique capabilities and its

broad potential– the experiments should capitalise on man’s presence– payload crew selection and training should permit the evaluation of future selection

and training criteria.

The principal selection criterion was, of course, scientific merit.


either totally NASA missions or from agencies that would pay the Shuttle/Spacelablaunch and operating fees.

ESA started to study in detail two European Spacelab missions, the so-called‘Demonstration Missions’. One of these was dedicated to microgravity studies in thelife and physical sciences, and the other to atmospheric physics (a pallet-only mission).The scientific, technical, operational and cost aspects of these two missions wererepeatedly presented to the ESA Spacelab Programme Board and proposed as anadditional slice to the Spacelab Programme. However, the Board, comprised ofDelegations from the ESA Member States, decided not to perform any further Spacelab missions under ESA management. The two main reasons for this refusal werethe large cost overruns on the Spacelab Programme, and the fact that the majority ofthe Member States did not want to spend major European funds on US Shuttle flights.

In the absence of an ESA Spacelab Utilisation Programme, Germany decided to carryout two German national Spacelab missions, D-1 and D-2. The German decision wasmotivated by a desire to utilise the European built Spacelab, towards which Germanyhad contributed 53% of the development costs of almost one billion Euros. It also wantedto have direct national access to space to perform materials-processing experiments ofindustrial relevance. The German space authorities invited ESA and interested MemberStates to participate in these German-led missions, in return for a contribution towardsthe Shuttle launch fees, based upon the proportional use of resources.

In the end, it was only ESA that took up this offer, once it had an approvedMicrogravity Programme. It participated in the D-1 mission with about 38% and in D-2 with about 25% of the payload. ESA also provided one of the three PayloadSpecialists for the D-1 mission (Wubbo Ockels).

- Early European Spacelab Experiment Facilities

From the overview of the Skylab and ASTP experiments and the replies to theEuropean Call for Experiments for the first Spacelab flight, it became evident thatmany experimenters required the same experimental facilities. For example, differentexperimenters required very similar furnaces, or they needed a 36°C incubator for celland developmental biology. To avoid the duplication of facilities and theiraccommodation requirements, it was evident that such facilities would have to bedeveloped with capabilities satisfying many users. These Multi-User Facilities, as theywere called, could therefore best be developed centrally. On the other hand, it seemedthat selected Principal Investigators (PIs) should develop any experiment-specifichardware or stand-alone experiments that were needed. They would obviously needfinancial support for this task, because the design, development and spacequalification of flight hardware was expensive.Consequently, ESA studied several multi-user research facilities at Phase-A level

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and the FPM, together with power- and data-management equipment, in one doublerack, called the Materials-Science Double Rack (MSDR).

The selected life-sciences experiments had a more heterogeneous technicalrequirement, because they belonged to very different life-science disciplines. Theseincluded radiation biology, cell biology, plant biology, a number of differentcardiovascular measurements and vestibular research experiments.

The vestibular experiments requested the most sophisticated facility, a Vestibular Sled.On the recommendation of the Life-Science Working Group, a conceptual design studyof the Sled was performed by ESA with the help of industry. All other experimentalhardware was to be provided by the Principal Investigators themselves, supported bytheir national space authorities.

After completion of the conceptual designs of these facilities, ESA proposed to thenational delegates of the Spacelab Programme Board that the development phase ofthese two multi-user facilities should be funded in one of two ways: either by creatinga new small microgravity research programme, or via a special new budget within theexisting Spacelab Programme. However, the Delegations could not agree to thisproposal and recommended that other solutions be sought by ESA.

A complicated solution eventually emerged, with the development of the Materials-Science Double Rack infrastructure taken over by Germany, together with two of thethree furnaces (isothermal and mirror furnaces). The Gradient Furnace was then to beprovided by France and the Fluid-Physics Module by Italy. Despite its many parents,this complex mix of equipment making up the Materials-Science Double Rack becamethe most important materials/fluids-science facility so far. It was flown on the twoGerman Spacelab missions, as well as on the first flight of Spacelab.


As shown in the accompanying table, the seventy experiments originated fromPrincipal Investigators in Europe (57), the USA (12) and Japan (1). The reason that manymore experiments from Europe were selected was mainly due to the fact that NASAwithdrew all of its material/fluid-science experiments from that first flight. They werescheduled for flight 9 months later on a US national Spacelab mission. The reason forthis change was formally the low amount of electrical energy and crew time availablefor the first flight. Also, at this time NASA considered materials-science experiments tobe sensitive investigations.

Analysis of the selected European materials-science and fluid-physics experimentsshowed that three types of furnaces would be needed. These were an isothermalfurnace, for the execution of 15 experiments, a gradient furnace for 5 experiments,and a novel mirror furnace for a further 5 experiments. A Fluid-Physics Module (FPM)would be needed for the execution of 6 experiments. ESA therefore initiated a detaileddesign study in industry with the objective of accommodating these three furnaces

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Figure 4.1.3. (a) The Materials-Science DoubleRack (MSDR), flown on the first Spacelab flightand again on the German D-1 and D-2missions. It contained two furnaces and severalinstruments supplied by Germany. Franceprovided a furnace and Italy a Fluid-PhysicsModule. (b) ESA astronaut Ulf Merbold picturedworking at the MSDR facility (courtesy ofMBB/DASA)

Figure 4.1.4. ESAastronaut Wubbo Ockelstesting the VestibularSled, used to studymotion and orientationperception inweightlessness

Materials Life Atmosph. Plasma Astro- Earth Technology Total

& Fluid Sciences & Solar Physics physics Observation +

Sciences Physics Environment

Europe 36 9 5 3 2 2 - 57USA - 7 2 1 1 - 1 12Other - - - 1 (J) - - - 1Total 36 16 7 5 3 2 1 70

The European experiments came from 10 ESA Member States.

(a)

(b)

division of responsibility, which is desired by ESA’s Member States on all ESAprogrammes, makes it necessary at the European level to co-ordinate the content andtiming of ESA’s programme with those of its Member States. It also requires the ESA-selected PIs to look for financial support in their home country. That has often meanta more severe experiment-selection process at ESA level, and additionally selection atthe national level for the financial support for the scientists.

The most recent national microgravity programme started in Europe is that of Italy.Due to Italy’s national contribution to the ISS infrastructure, in the form of the Multi-Purpose Logistics Module, it has acquired independent utilisation rights for the use ofthe ISS. As a result, the Italian initiative is principally concerned with the nationalmicrogravity experiments that are to be performed on the ISS. The focus ofmicrogravity research in Italy has been on fluid physics, and that emphasis tends tobe reflected in the type of experiments destined for the ISS. An Italian centre dedicatedto microgravity research (MARS) has been established in Naples. In addition, Italyplans to develop a mouse holding facility for use on the ISS. Italy has always been amajor investor in the ESA Microgravity Programme. Its industry has been very activein developing ESA’s multi-user facilities in the fluid-physics field, and in thedevelopment of sounding-rocket payloads for ESA.

In Sweden, the national microgravity programme has evolved around the sounding-rocket activities. Flight-hardware development has focused on experiment modules forthe nationally initiated Maser sounding-rocket projects, and on launch-operationssupport for the Texus and Maxus sounding-rocket flights. All of the Europeanmicrogravity-dedicated sounding rockets are launched from the Esrange centre, nearKiruna in the north of Sweden. The Karolinska Institutet continues to carry out spaceexperiments in the life sciences, particularly on respiratory physiology.

Belgium has always strongly supported ESA’s Microgravity Programme phases. It haspromoted, within the framework of the ESA General Supporting TechnologyProgramme, several microgravity-dedicated projects at the national level. AMicrogravity Research Centre has been established at the Université Libre de Bruxelles.

Switzerland, Denmark and Spain have always contributed to the various phases of theESA microgravity programme. At present, the emphasis of microgravity-relatedresearch in Switzerland has been put on cell and developmental biology, together withbiotechnology. In Denmark, the emphasis is on human physiology, at DAMEC. InSpain, the interest lies largely in fluid science, protein crystallisation anddevelopmental biology.

In the Netherlands, there has been continuing active scientific interest in the ESAprogrammes, with varying levels of financial support. The United Kingdom andNorway have each supported the programmes at various times and at modest levels.


The solution found for the development of the Vestibular Sled was an ESA internal one.The conceptual and detailed design of the Sled was covered financially by the ESAGeneral Budget, whereas the actual development was, exceptionally, financed by theESA Space Science Programme.

The Sled was designed to perform selected studies on man’s perception of orientationand motion in the microgravity environment, from cues provided by the vestibularreceptor system, the visual system and the mechano-receptors in the skin and joints.It was a movable sled mounted on 3.2 m-long rails and provided linear accelerationstimuli as a result of pre-programmed velocity trajectories. The astronaut riding on theSled wore a Vestibular Helmet, which included a small television screen and aninfrared camera to record the astronaut’s eye movements.

In fact, the Sled did not fly as planned on the first Spacelab mission, but on thesubsequent German Spacelab flight D-1. The reason was that the final payload massfor that first flight was going to exceed substantially the allowed mass. A large facilityhad to be removed and the Sled was chosen. Although its flight was thereby delayedfor two years, it did ultimately provide valuable results for the 11 European and 10US/Canadian researchers.

4.1.3 The European National Programmes

The difficulties and delays associated with the creation of the ESA MicrogravityResearch Programme have been outlined above. At the national level, however, severalof the ESA Member States had been developing their own microgravity researchprogrammes since the 1970s. This was especially the case for Germany, and to a lesserextent for France and also for Sweden (only sounding-rocket missions). Germany andFrance developed microgravity research communities, designed and developedexperimental facilities and executed Spacelab missions (Germany), and/or sounding-rocket flights (Germany and Sweden). They also used Soviet flight opportunities(France, Germany and Austria) to fly microgravity experiments and astronauts. Franceand Germany also used the Russian Foton unmanned retrievable capsule.

There is one key difference between the ESA Microgravity Programme and those of theUSA, Japan, Canada or the national programmes of the ESA Member States. That is, itdoes not include any means to provide substantial support to perform ground-basedpreparatory research for the experiments of ESA-selected Principal Investigators/Co-Investigators (PIs/CoIs). This PI/CoI-funding responsibility normally falls upon thenational space programmes or upon other national research funding institutions suchas Ministries, Universities, etc. This means that ESA’s microgravity activities, whichinclude the definition of priority research fields, the solicitation and selection of flightexperiments, provision of flight opportunities, and flight hardware at multi-user facilitylevel, have to be complemented by national funding for the work of the PIs/CoIs. This

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After detailed studies of short-duration flight opportunities, the decision was taken in1976 to set up the Texus sounding-rocket programme, as a preparatory endeavour forthe upcoming Spacelab utilisation era. The Texus programme actually exceeded, interms of reliability and experimental facilities, the contemporary American Spar andJapanese TT-500A sounding-rocket programmes. Texus is still going today and is the‘workhorse’ of the German microgravity programme, being continuously used by bothESA and DLR. The Texus programme holds a record of 36 successful flights since 1977,the year of the first lauch. It has developed into an independent research opportunityin microgravity. Advanced operational features like remote tele-operation/telesciencewere introduced at an early stage in 1983, enabling experiment control to beperformed from the Microgravity Support Centre (MUSC) at DLR, Cologne, to thelaunch site at Esrange in northern Sweden.

As part of its contribution to the effective utilisation of Spacelab (see Section 4.1.2), theGerman national programme provided major multi-user facilities to the Spacelab-1(FSLP) flight in 1983. One was the Materials-Science Double Rack (MSDR), which wasalso re-flown as a major payload element on the two German D-1 and D-2 Spacelabmissions in 1985 and in 1993, respectively. The MSDR was the first materials-sciencepayload element developed in Europe, and it contained the following German-developed facilities:– Isothermal Heating Facility, dedicated to metallurgical investigations– Mirror Heating Facility, for the crystallisation of semiconducting materials– High-Temperature Thermostat, for diffusion studies in metallic melts– Cryostate, for protein-crystallisation experiments.

In addition, the Gradient Heating Facility from France and the Fluid-Physics Moduledeveloped in Italy were accommodated in the MSDR. For all of these experimentalfacilities, the MSDR provided joint power conditioning, heat rejection, and datamanagement.

The MSDR (Fig. 4.1.3) was developed within the German Microgravity Programme andoffered to ESA for European utilisation. It accommodated ‘Cryostate’, in which the firstprotein crystals were grown in space, an event that initiated a worldwide proteincrystal-growth programme in space.

Another contribution to Spacelab-1 was the ‘Integrated Helmet’, for vestibularresearch, using a video-oculograph method. Vestibular research, as part ofneurological sciences, is an important field of emphasis within the GermanProgramme. An advanced version of this facility is presently under development forthe International Space Station.

Highlights of the German Microgravity Programme have been the two GermanSpacelab missions D-1 and D-2, which were primarily dedicated to microgravity


Recently, this situation seems to be changing as far as the UK is concerned, with theinclusion of applications-oriented research (MAPs) in the ESA programme.

Austria did not participate in ESA’s Microgravity Programme phases. It did, however,carry out a life-sciences-dedicated mission to Mir, in co-operation with the Russianspace authorities.

The national microgravity programmes of both Germany and France are large. Theyhave carried out national missions, built substantial dedicated facilities andequipment, and selected and supported their experiments. The following is an outlineof the relevant major activities in each of those countries.

- The German Microgravity Programme

Germany started its first microgravity research activities in 1972, with programmaticstudies and the preparation of some experiments in the fields of biology, materialsscience and biotechnology. The early development of the experiment ‘Biostack’, in thefield of radiation biology, is noteworthy. This device was first flown on Apollo-16 and -17, with many subsequent re-flights. Derivatives of this outstanding facility are still inuse. In addition, several materials-science experiments have been performed onSkylab.

A principal motivation for Germany to create its own Microgravity ResearchProgramme was the European decision, in 1973, to develop Spacelab as itscontribution to NASA’s post-Apollo Programme. Germany contributed 53% to theSpacelab Programme. Consequently, it intended to prepare for the scientific andapplications-oriented utilisation of Spacelab. Already in 1975, the Federal Ministry forResearch and Technology (BMFT) established five discipline-oriented planning groupsof scientists from academia and industry to prepare plans for the utilisation ofSpacelab in materials/fluid sciences and applications. Three planning groups weresimilarly established to cover the life sciences. The outcome was that the BMFTapproved a broad Spacelab utilisation promotion programme. Some 50 projects werecontained within that programme, including the preparation of experiments.

Another milestone in the early German microgravity programme was the performanceof three free-flow electrophoresis experiments on the Apollo-Soyuz mission in 1975, asmentioned earlier.

In these early days of microgravity research, German scientists participated in theAmerican Spar sounding-rocket programme. Experiments were concerned withinvestigating the separation process in monotectic alloys. It was as a result of theseexperiments that the important role of Marangoni convection in such processes wasdiscovered.

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Columbus Laboratory. In co-operation with ESA, the German programme is providinga key part of the MSL-EML facility in the form of the automatic experiment-exchangechamber (see Section 5.2 for details).

For the last Spacelab mission, Neurolab in 1998, Germany provided a collapsibleLower-Body Negative-Pressure Device for co-operative research on this mission. Inaddition, the Aquatic System CEBAS, first flown on STS-89 in1998, was re-flown.CEBAS is a nearly closed, aquatic ecological system with water plants, fish and snails,which allows investigations in developmental biology and ecological stability. It is tomake a third flight on the STS-107 Spacehab mission in 2002.

Two German missions to Mir were performed in 1992 and in 1997. German astronautswere also flown on these missions, mainly to support research in human physiology,which was their focal point. Medex, a cardiovascular research facility, should bementioned in this context. Germany also provided the Titus furnace and vestibularresearch equipment (VOG) for the Euromir ’94 and ’95 missions.

Germany has participated with experiments (about 10% of the payloads) in sevenFoton missions, starting with the Foton-7 in 1991. Since 1982, the German programmehas also flown 19 ‘Maus’ facilities, which are small autonomous standardisedexperiment facilities carried in the Shuttle’s cargo bay.

Spacehab was used for the first time in 1996 (on STS-77) with a modified MirrorHeating Facility (ELLI) in a German-Canadian co-operation. The next experiments wereperformed in 1998 (on STS-89 and STS-95), and further experiments are planned ontwo future Spacehab missions (on STS-107 in 2002 and STS-112 in 2003).

In addition, further short-duration experiment facilities, such as the Drop Tower inBremen and the Microba (Payload Drop Facility from a 40 km altitude balloon), weredeveloped as part of the German microgravity research programme. The Brementower has become the most extensively used drop facility in Europe.

Germany contributed 53% of the cost of the ESA Eureca development programme. Alarge portion of the 28 European experiments on Eureca also came from Germany, i.e.the German national programme supported many Eureca PIs (see Section 6.7).

Utilisation of the ISS within the German national programme is supported bydeveloping a number of instruments. These include the Lower-Body Negative-PressureDevice (LNBP), a second-generation eye-tracking device for vestibular research, andCardiolab, in co-operation with CNES, a major element of the European PhysiologyModule (EPM). The EPM is one of the four large ESA facilities under development foraccommodation in the Columbus Laboratory. One of the first experiments on theInternational Space Station is the German– Russian Plasma Crystal Experiment (PKE),


research. These missions provided research opportunities not only to Germanscientists, but also to other European investigators, mainly via ESA’s participation.

Based on scientific requirements, Germany has developed equipment especially forinvestigations in the following research fields: – Fundamental Physics: Capillarity, Marangoni Convection, Diffusion, Critical Point

and Heat Transfer– Materials Science: Solidification Front Dynamics, Composites, Crystal Growth

Undercooling and Nucleation, Technologies– Life Sciences: Neurophysiology, Cardiovascular System, Pulmonary System,

Endocrinology and Metabolism, Cognitive Behaviour, Bioprocessing/Biocrystals,Cell Cultivation, Gravisensitivity, Radiation Biology and Exobiology.

The outcome of these missions included important new findings, which are publishedin the relevant scientific literature and in special publications on the D-1 and D-2missions. Both missions were performed with the intensive application of tele-scienceand tele-operations from the German Mission Control Centre at DLR.

After D-1 and D-2, Germany participated in the international NASA Spacelab missionsIML-1 (1992) and IML-2 (1994), with major contributions. In the field of gravitationalbiology, a multi-user facility with novel features was developed. In ‘NIZIMI’, amicroscope is accommodated on a slowly rotating centrifuge, allowing measurementsof the biological threshold of gravity sensitivity. Also for this mission, and since re-flown twice on MSL1/1R (1997), thetechnologically very complex Tempusfacility (see Section 5.2) was developedfor the accurate determination of thethermo-physical properties of alloys ofindustrial relevance and for undercoolingexperiments. This unique Tempus facility(see Fig. 4.1.5) is the predecessor of theMSL-EML (Materials-Science Laboratory -Electromagnetic Levitation facility)planned for accommodation in the

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Figure 4.1.5. The German ‘Tempus’Experiment Module. Electromagnetic

levitation allows high-temperaturereactive melts to be studied without

having to use a container. An ESA follow-on development of this system will be

used in the ISS/Columbus MaterialsScience Laboratory (courtesy of

Astrium/Dornier)

resulted – at moderate cost – in a growing number of research teams with excellentscientific expertise.

In the Physical Sciences, French national microgravity research concentrated mainlyon the following areas:– solidification (improvement of the microstructure due to the absence of gravity and

study of instabilities at the liquid/solid interface)– crystal growth (especially from solutions, protein crystallisation)– measurements of thermo-physical coefficients– critical-point research– combustion.

In support of this research, CNES has used ESA flight opportunities and ESA’sexperiment facilities, such as the Advanced Gradient Heating Facility (AGHF), theCritical-Point Facility (CPF), the Advanced Protein-Crystallisation Facility (APCF), etc.(see Table 6.2) and ESA sounding-rocket experiment opportunities. In addition,however, at the national level CNES developed some highly sophisticated researchinstruments and flew them under bilateral arrangements with NASA and with theRussian space authorities. The most important of these nationally developedinstruments are:– Mephisto, a furnace in which the Seebeck effect is used to characterise the status of

the solid/liquid interface. This instrument was flown several times on NASASpacelab pallet missions in the 1990s.

– Alice-1, an instrument with capabilities similar to those of ESA’s earlier developedCritical-Point-Facility (CPF) for Spacelab and sounding rockets. It was accommodatedon Mir, in the framework of French missions in the period 1992 – 96. Alice-2 wasused from 1996 onwards. Alice-1 and -2 employed optical and very precise thermaldiagnostics to support critical-point research. These studies resulted in the discoveryof a new heat-transfer mechanism, which is due to the adiabatic heating of fluids bydilatation of limited thermal layers. It is called the ‘Piston Effect’ (see Section 2.3.5).This new heat-transfer mechanism has already found industrial application (AirLiquide) in the storage of cryogenic fluids on Ariane-5.

In addition, CNES has supported the development of two short-duration flightopportunities:– the Drop Tube in Grenoble, to support mainly short-duration solidification and

combustion studies– parabolic aeroplane flights, using first a Caravelle and later an Airbus-300 aircraft

(flights managed by Novespace, a company set up by CNES).

In the Life Sciences, the French national programme did not simply limit its activitiesto supporting its science teams that were using ESA flight opportunities andexperimental facilities. CNES also concluded – especially after the Challenger accident


which has been developed in the German Programme. PKE is a pilot experiment for theplanned International Microgravity Plasma Facility (IMPF) for the ISS (see Section2.3.8). Germany will also contribute a key element of the Materials Science Laboratory(MSL–EML) facility, as detailed later.

From a programmatic point of view, it is noteworthy that, in the 1980s and early1990s, the financial envelope of the German national microgravity programme(excluding the mission costs for Spacelabs D-1 and D-2) was larger than that of ESA’smicrogravity programme. However, this envelope was reduced from about DM 100million/year in 1990 to about DM 40 million/year in 1998, and is planned to remainconstant until 2003. This reduction in the national microgravity research budget iscompensated by an increasing German contribution to the ESA microgravityprogramme in the 1990s, so that the overall level of activity in the German scientificcommunity and in the relevant space industry was not reduced. In the 1990s,European space industry and especially German space industry, which developedsophisticated experimental facilities for the ESA and German microgravityprogrammes, was recognised as a world leader in this field. German industry createdthe European entity ‘Intospace’ in the mid-1980s, which was later supported by nearly60 European firms, to facilitate industry’s access to flight opportunities.

- The French Microgravity Programme

The financial envelope for France’s space activities, consisting of its contribution toESA’s space programmes and the national space projects, makes it the largest investorin space in Europe. Within the ESA framework, France contributes the largest share ofall ESA Member States to Ariane, the biggest of the European space programmes. Alsoat the national level, France’s space programme, which is administered by the Frenchspace agency CNES, exceeds that of any other European country.

France’s leading position in terms of European space expenditure is not, however, fullyreflected in its funding of microgravity research. The French contribution to ESA’sMicrogravity Programme has, on average, been about half that of Germany and aboutthe same order of magnitude as that of Italy. The financial envelope of the nationalmicrogravity programme in the 1980s was considerably smaller than that ofGermany. This situation changed somewhat in the first half of the 1990s, but duringthe second half the national microgravity activities had a low priority amongst theFrench space programmes. Only in 2000 was this low-priority status revised.

Despite these political and financial circumstances, a motivated and competitivephysical- and life-sciences community has developed in France. The nationalprogramme was predominantly oriented in the past towards basic research. Thescientific projects selected were co-ordinated with ground-based preparatory researchand only clearly space-relevant topics were selected for in-orbit experiments. This

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– in gravitational biology, radiation biology and exobiology: developmental biologystudies on, for example, amphibian eggs (pleurodels), plant gravitropism andgravimorphism, physical and biological dosimetry, induction of lesions at thegenomic level and their mutational consequences.

For many of these studies, special experimental hardware was developed within theFrench national microgravity programme. These items included ‘Cognilab’(perception), ‘Physiolab’ (cardio-vascular physiology), ‘Kinelite’ (movement problems),‘Fertile’ (developmental biology), and ‘Ibis’ (cell and developmental biology).

Utilisation of the International Space Station within the French national microgravityresearch programme is planned in the physical- and life-sciences areas. In continuingresearch on critical-point phenomena in the ISS, the CNES will develop the ‘Declic’instrument, which is designed to study high-temperature critical fluids and thecrystallisation of transparent materials.

As is explained in Section 5.2, CNES, in co-operation with DRL, will develop animportant element called ‘Cardiolab’ for the ESA ISS laboratory’s European PhysiologyModules (EPM). Cardiolab is derived from the French Physiolab and the GermanMedex, both of which were developed for and flown on Mir.

A long-term plan of CNES is the development of a Neurosensory Research Laboratory(SENS), which will include existing instruments such as the Kinesigraph, theOcculometer, Cognilab and new stimulation devices


in 1986 – bi-lateral arrangements with the Soviet/Russian space authorities toperform joint missions to Mir.

There was a first mission, with the first French astronaut, to Salyut-7 in 1982. This wasfollowed by several missions to Mir between 1988 and 1999:– Aragatz, 1988, 25 days duration– Antares, 1992, 14 days duration– Altaïr, 1993, 21 days duration– Cassiopée, 1996, 16 days duration– Pegase, 1998, 20 days duration– Perseus, 1999, 6 months duration.

These missions were predominantly used to perform human-physiology studies onFrench and Russian astronauts, but some gravitational biology, exobiology, andcritical-point studies were also conducted.

In addition, some nationally selected life-sciences experiments were performed onNASA’s Spacelab missions IML-1, IML-2 and LMS, and on Russian Foton/Bionretrievable pressurised-capsule missions.

The major scientific topics addressed during these space missions on man andanimals were:– in neurosciences: the adaptation of the sensori-motor functions, movement and

posture, cognition aspects such as perception, memory and spatial orientation.– in cardiovascular physiology: cardiovascular deconditioning, with studies in

haemodynamics, control of arterial blood pressure, hormonal mechanisms in bloodand total body-fluid loss, cerebral fluid, etc.

– in the field of bone modifications and muscle degradation: bone-density changes inastronauts and osteoporosis in animals, muscle atrophy and modifications ofmuscles in microgravity

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Figure 4.1.6. The French‘Mephisto’ furnace, usedfor detailed study of thesolidification processes atthe melt solid/liquidinterface and flown onseveral Spacelab palletmissions (courtesy ofCNES)

In order to improve the situation and to provide a strategy and plans for the future,ESA again proposed to its national Delegations the creation of a Microgravity ResearchProgramme. Among its stated intentions was the selection of investigations accordingto scientific-merit criteria, the development of the necessary multi-user facilities andthe payment of space mission costs (i.e. payload integration, launch fees andoperation costs).

In the ensuing discussions, the ESA-proposed budget to cover those activities overseveral missions was substantially reduced by the Delegations. It was limited to aprogramme to cover just an ESA participation to supply and fly certain multi-userfacilities on one Spacelab mission, namely the German D-1 mission, and to prepare therelated experiments on the equivalent of four Texus sounding-rocket missions withESA payloads, spread over seven Texus flights. Nonetheless, it was a step in the rightdirection, as it opened a way ahead for microgravity research on a European basis.

This Phase-1 of the ESA Microgravity Programme formally got underway in January1982, with a financial envelope of 48.6 MAU spread over the years 1982 to 1986 (theAU was roughly equivalent to 1 US Dollar; it was an ESA internal budget predecessorof the Euro). The participating Member States were: Germany (38.2%), France (21.4%),Italy (10.4%), Belgium (6.2%), Sweden (5.9%), Switzerland (5.6%), the Netherlands(5.5%), Denmark (3.5%), the United Kingdom (1.9%) and Spain (1.4%)

There were three Phase-1 programme elements:– Biorack, a multi-user facility to be built for investigations in the field of cell and

developmental biology and flown on the D-1 Spacelab mission. During that flight,Biorack supported the execution of 14 experiments. It later became the multi-userfacility with the highest flight frequency, flown on three Spacelab and three Spacehabmissions.

– The Improved Fluid-Physics Module (IFPM), an improved version of the originalFluid-Physics Module flown on the first Spacelab flight. It was designed to studymainly phenomena connected with the hydrodynamics of floating zones andMarangoni convection. It was flown on the D-1 mission and eight selectedexperiments were conducted.

– The Sounding-Rocket Programme Element, which involved ESA in developing the experiment modules equivalent to four Texus payloads, each weighing 240 kg. Thisbegan with the Texus-6 mission in 1982.

In parallel with these Phase-1 programme elements, ESA developed the VestibularSled, as mentioned earlier.

The flight of the three ESA facilities – the Vestibular Sled, Biorack and the IFPM –amounted to 38% of the total payload of the German D-1 Spacelab mission, in termsof utilisation of the critical resources (mass, crew time and electrical energy). The ESA


4.2 The ESA Microgravity Programmes

4.2.1 Towards the First ESA Microgravity Programme (Phase-1)

By 1980, the lack of a coherent overall European strategy and programme for thedevelopment of microgravity research and the use of the European-developedSpacelab was clearly unsatisfactory and becoming untenable. The solution to theproblem of funding the facilities for the first Spacelab flight with a complicated mix ofnational funds and ESA funds from other programmes, was not a viable arrangementfor the future, for several reasons:

– Interest in performing life- and physical-sciences experiments in space increased inthe late 1970s in all of the ESA Member States, as evidenced by the fact that theexperiments selected for the first Spacelab flight came from 10 different MemberStates. During the discussions on future Spacelab missions, the national delegationshad considered it fair that all Member States from which Principal Investigators hadbeen selected should contribute to facility development/refurbishment costs and tointegration and operation costs. However, when Germany offered other ESAMember States the opportunity to participate with their own national experimentsin the D-1 mission on a cost-reimbursable basis, none were willing to make use ofthis opportunity. There were, however, a few co-operative experiments flownwithout a contribution to the D-1 mission costs.

– Apart from the Vestibular Sled, the multi-user facilities that were developed for thefirst Spacelab flight did not serve the important but crew-intensive research fields,such as cell and developmental biology or the broad field of cardio-vascular andcardio-pulmonary research. This was because the crew time available for thescientific payload on the first verification flight was limited to 100 hours.Consequently, the centralised development of the multi-user facilities, such asBiorack and Anthrorack, which were needed to support such research, waspostponed to later missions. Yet neither Germany, nor any other Member State, waswilling to develop such facilities at a national level, if they were to be used byPrincipal Investigators from other Member States on later missions.

– A similar situation existed for the case of certain sub-disciplines in fluid physics andmaterials sciences. Based upon the requirements of proposed experiments, therewas a need to develop a Critical-Point Facility, a Bubble Drop and Particle Unit and amulti-user Protein-Crystallisation Facility. For these facilities also, no nationallyfunded developments were offered.

– Since 1977, German scientists had been able to prepare for microgravityexperiments on Spacelab by conducting precursor experiments on short-durationrocket flights. The German national space programme funded those Texus rocketflights. Principal Investigators from other Member States usually did not haveaccess to such preparatory flight opportunities, apart from a few bilateralcooperative experiments.

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The reflight, upgrading, and refurbishment costs for the Biorack and Sled were alsoexamined.

In meetings at that time, ESA explained to NASA that the very high Shuttle/Spacelabtransportation costs, representing more than half of the Spacelab utilisation costs,posed a major barrier to the further development of the European microgravityresearch programme. It made it impossible for ESA to obtain agreement from itsMember States for the funding of a reasonable European Microgravity Research and Spacelab Utilisation Programme, despite the fact that ESA had spent about1 billion AU (Euros) on the development of Spacelab, which NASA was using. TheMember States were simply unwilling to spend huge amounts of money on Shuttlelaunch fees.

These ESA–NASA discussions finally led to the generation of a series of NASA Spacelabmissions called ‘International Microgravity Laboratory’ or IML missions, in which ESAcould participate. The IML agreement required that ESA would develop some multi-user facilities of a high technological standard for Spacelab that fulfilled NASA’stechnical performance requirements as well as those of the ESA-selected experiments.NASA and ESA would then use the resulting facilities on a 50/50 basis, and in returnNASA would fly these ESA facilities on an IML-mission at no cost to ESA. However,agreement had to be reached for each facility separately. NASA would accept themonly if it had no equivalent facility type, or if the ESA facility had a higher performance.Also, for the ESA facilities for which there were no NASA-selected experiments, ESA hadto pay the Shuttle mission fees.

This agreement was a major breakthrough in the process of establishing a new, larger,and more coherent ESA Microgravity Research Programme. It was an agreement thatalso applied later for NASA’s LMS and Neurolab Spacelab missions. The result was thatESA could establish the larger Phase-2 Microgravity Programme. It was approved inFebruary 1985, with a financial envelope of 131 MAU, to cover four years. Twosubsequent large extensions to this Phase-2 Programme took place in 1988 and 1991,as discussed in detail below, and led to an envelope of almost 600 MAU, spread overthe period 1986 – 1998.

This Phase-2 Programme permitted the development of all of the facilities (except theBotany Facility) that had previously been studied:– AFPM, BDPU and CPF in the fluid-sciences field – AGHF and APCF in the materials-science field, and– Anthrorack in the human-physiology field

together with the reflight of Biorack and the Vestibular Sled and also three furtherprogramme elements:– short-duration flight opportunities (mainly sounding-rocket flights)


Phase-1 programme paid the NASA launch fees for Biorack (15%) and the IFPM (5%),based upon the use of these critical resources during the D-1 mission. The launch fee forthe Sled (18%) was paid by the German space programme, under an earlier agreement.

4.2.2 Phase-2 of the ESA Microgravity Research Programme and Its Extensions(EMIR-1)

The few facilities that were developed within the framework of Phase-1 of the ESAMicrogravity Programme could serve only a small part of the interests of Europeanmicrogravity research scientists. ESA therefore continued to study the technical andcost aspects of additional multi-user facilities in detail during the period 1982–84.These facilities included:– an Advanced Gradient Heating Facility (AGHF)– a Critical-Point Facility (CPF)– a Bubble Drop and Particle Unit (BDPU)– an Advanced Protein Crystallisation Facility (APCF)– an Autonomous Fluid-Physics Module (AFPM)– a facility for human-physiology research (Anthrorack)– a Botany Facility (BF).

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Figure 4.2.1. The ESA ‘Biorack’, whichaccommodated 14 cell and developmentalbiology experiments on the Spacelab D-1mission and was later used on the twofurther Spacelab and three Spacehabmissions. ESA astronaut Wubbo Ockels isseen here working at this facility

Figure 4.2.2. TEM-EVA, one of theexperiment modules for Texus soundingrockets (Texus-38)

the above Programme elements and the stretching of the development of the Phase-2multi-user facilities. The duration of the combined Phase-2 plus First Extension wasprolonged by 3.5 years, until the end of 1992.

A Phase-2 Second Extension took place in late 1990, because new flight opportunitiesbecame available on:– NASA Spacelab missions (IML-2, USML, LMS)– the German D-2 Spacelab mission– Russian retrievable satellites (Foton)– Maxus sounding rockets (from 1993 onwards, with a large payload-carrying

capability of 440 kg and up to 13 min of microgravity conditions)– Spacehab (offered as part of the barter agreements with NASA for Biorack and APCF

use)– Get-Away Specials (GAS) in the Shuttle’s Cargo Bay.

These Spacelab missions meant flight opportunities for the multi-user facilities thenunder development, like CPF, BDPU, AGHF, and re-flights for Biorack, as well asopportunities for new multi-user facilities to be developed such as: – Biobox, Biopan and autonomous experiments for Foton missions– a Respiratory Monitoring System (RMS) for the D-2 Spacelab mission and a second

generation of it (RMS-2) for Euromir ’95– Bone Densitometer as well as blood kits and stand-alone physiology and radiation

experiments on the Euromir missions– Glovebox for the USML-2 Spacelab mission– Torque Velocity Dynamometer for the LMS (Life and Microgravity Sciences) Spacelab

mission– Diffusion-Coefficient Measurement Facility for a GAS (Get-Away Special) payload on

Shuttle flights.

This Second Extension of Phase-2 further prolonged its duration until the end of 1995,i.e. by another 3 years, and increased the approved financial envelope from 203.8 to336.2 MEuro (at 1983 economic conditions). With the consent of the MicrogravityProgramme Board, this envelope was later exceeded by a cost overrun of 14%. Thiswas due to further delays in Spacelab missions, the need to cover further developmentof Euromir equipment, and the payments for a part of the mission costs for Euromir’95 (ESA Euromir missions were not yet planned when the Phase-2 Second Extensionwas approved).

From 1993 onwards, this Phase-2 and its two extensions were formally known as EMIR-1, or European Microgravity Research Programme 1. The total financialenvelope for the EMIR-1 programme, invested over a period of about 14 years (1985– 1999), was 598 MEuro at current price levels (i.e. in the economic conditions of theyear in which the money was spent).


– 20% use of German multi-user facilities on the D-2 Spacelab mission– a Microgravity Supporting-Technology Programme.

The Phase-2 Programme was supported by 11 ESA Member States, with the followingindividual participations: Germany 35.00%, Italy 17.00%, France 16.80%, Belgium4.50%, The Netherlands 4.00%, Switzerland 3.87%, Sweden 3.44%, Spain and theUnited Kingdom each 2.00%, Denmark 1.98%, and Norway 0.50%.

Since there was still an under-subscription of about 9% in terms of the totalprogramme cost, it was agreed to shift the planned development of the Botany Facilityto a later programme phase. In addition, the proposed reflight of the Sled wascancelled, after NASA refused to fly it under the IML agreement. The problem was thatthis large 550 kg facility would have disturbed the microgravity environment neededby other experiments when it moved along Spacelab’s aisle.

During 1985, ESA had placed the development contracts with industry for most of thenew multi-user facilities. Then in January 1986, the Challenger disaster occurred. Theresult for the ESA Programme was a gap in Shuttle flight opportunities that lastedalmost six years. It was not until January 1992 that ESA again had access to Spacelab,when the IML-1 mission with some ESA microgravity-science payloads was flown. TheGerman D-2 mission had to be postponed from its planned launch date in 1988 untilApril 1993, a delay of about five years.

To try to reduce the negative impact of the Challenger accident on the microgravityresearch of the European science community, ESA stretched the on-going industrialdevelopment contracts and restructured Phase-2 of its Microgravity Programme asfollows:– It increased the short-duration flight opportunities, by doubling the flight frequency

of sounding rockets and by adding preparatory parabolic airplane flights and byenabling experiments on drop towers.

– It started to perform biological experiments on the Soviet Bion (later called Foton)unmanned, but pressurised, retrievable satellites. (The Soviet space authorities didnot offer the use of Mir or Bion/Foton for ESA materials/fluid-science experiments atthat time).

– ESA began a ‘General Activities Programme Element’ to cover the Phase-A and -B(design and costs) studies of microgravity research facilities for the ESA ColumbusLaboratory of the International Space Station, i.e. the preparation of the later MFC-Programme.

A Phase-2 Programme Extension was an evident requirement, due to the delays in thelaunch dates for the Spacelab IML-1 and D-2 missions. When, in November 1988, theextent of these delays became firmer, Phase-2 was extended financially from theoriginal 131 MEuro to 203.8 MEuro (at 1983 economic conditions). This was to cover

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period 1993 – 1996 was 226, whereas the corresponding number for the four-yearperiod 1999 – 2002 is only 72. This is a drastic reduction in experimental activities,which has hampered progress in ISS utilisation preparations. This effect wasaggravated by the fact that no co-operative NASA/ESA agreements existed, such asthose for the Spacelab missions between IML-1 (1992) and Neurolab (1998). All flightcosts for sounding rockets, Foton and Spacehab missions had to be covered by theEMIR Programme.

The halving of the annual budget for EMIR-2, compared to the mid-1990s, and theneed to procure all flight opportunities after the termination of co-operative Spacelabflights by NASA in 1998, proved to be a major drawback in terms of adequatepreparation for the utilisation of the ISS.

However, a positive effect on the preparation of ISS utilisation in the years 1999 – 2002is being provided by the Columbus Utilisation Promotion Programme. Themicrogravity part of this programme addresses researchers from industry andacademia for developing relevant Microgravity Application Promotion (MAP) projects.MAP is intended to develop pilot projects demonstrating that the ISS is a unique toolwith which to advance terrestrial research with industrial objectives. MAPs aresupported by ESA, national space agencies and industry. The funding share of industryis unexpectedly high, i.e. about 1/3 of the total funding requirements of about 40 MAPprojects selected in the frame of two Announcements of Opportunity (AOs) for MAPprojects in the physical and life sciences. The residual funding is shared by ESA (onethird) and the institutes/national agencies (one third each).

The contribution from ESA’s Columbus Utilisation Promotion Programme to MAPprojects is about 28 MEuro. This Columbus Utilisation Promotion budget approval wasa single event, which was not continued by a follow-on approval of a promotionbudget at the Brussels Ministerial Conference in 1999. Consequently, this verypromising active co-operation of non-space industry might come to an end after 2002,i.e. some years prior to the start of the routine phase of ISS utilisation. Therefore, anESA contribution to MAP projects needs to be continued after 2002, if industrialresearch on the ISS is to be seriously encouraged.

Figure 4.2.3 shows in graphical form the annual budgets of the various microgravity-research-related programmes from 1982 onwards. It also demonstrates that,considering that the development of experimental facilities takes about 3 to 4 years, adecision on a microgravity follow-on programme is needed in late-2001.

Since the completion of ISS assembly is presently expected at the end of 2004/early2005, routine utilisation will not start before 2005. With present approved funding(Figure 4.2.3), there will be a three year gap in ESA’s microgravity research prior to ISSutilisation, unless a new life- and physical-sciences programme is approved to allow


4.2.3 The ESA EMIR-2 Programme, Its Extension and Applications Projects

The objective of the EMIR-2 programme was to maintain an active microgravity usercommunity until the start of utilisation of the International Space Station. At the timein 1995 when the EMIR-2 programme was proposed, ISS utilisation was foreseen tocommence in 2001.

The proposed EMIR-2 basic programme consisted of a number of specific activitiessuch as:– continuation of Mini-Missions, including sounding rockets, parabolic airplane

flights, drop-tower/tube experiments– experiments for retrievable carriers (e.g. Foton) using Biobox, Biopan, Fluidpac and

furnaces– utilisation of manned systems (Spacelab, Spacehab, Mir and, when launched, the

US-Lab of the ISS). The facilities to be developed for these research opportunitiesincluded:• the European Modular Cultivation System (EMCS) for plant and cell biology• the Protein-Crystallisation Diagnostics Facility (PCDF)• the Space-Exposure Biological Facilities (Matroshka and Expose)• the Advanced Respiratory Monitoring System (ARMS)• the Facility for Absorption and Surface-Tension Studies (FAST)• the reflights of the Advanced Gradient Heating Facility (AGHF) and the

Advanced Protein-Crystallisation Facility (APCF)

ESA’s programmatic proposal for EMIR-2 was only partially approved at the 1995Council Meeting at Ministerial Level. Nevertheless, an amount of 153 MEuro (1995economic conditions) was approved. This enabled the continuation of the basicutilisation activities, at a reduced level of about 35 MEuro/year, for a period of 4 years,i.e. until 2001.

The basic EMIR-2 utilisation programme had an annual financial envelope only abouthalf that of its predecessor programme EMIR-1, during the first half of the 1990s.However, the start of the ISS routine utilisation phase was successively delayed, beingmoved finally into the 2005 time frame. Consequently, in 1999 ESA tried to obtain anincrease in the financial envelope of the EMIR-2 programme to cover this gap, byproposing an EMIR-2 Extension. At the request of its Member States, ESA reduced thecost of this Programme Extension several times, so that the final approval coveredonly an amount of about 50 MEuro.

The consequence of this neglect of flight/research opportunities in the pre-Columbusera is demonstrated in Figure 6.5.1, which shows many fewer experiments beingperformed each year in the period 1999 to 2002, compared with the mid-1990s. Asshown in the Appendix, in Table 6.7, the number of experiments flown in the four-year

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Columbus Free-Flying Laboratory. These facilities were afterwards studied technicallyand from a cost point of view by ESA, with the support of European space industry.

The multi-user facilities for the Columbus Attached Laboratory and the Columbus Free-Flying Laboratory studied at the time were as follows:

As a result of a cost-reduction exercise, the size of the Columbus Attached Laboratorywas reduced from an originally 12.8 m-long cylinder, to one 6.4 m in length and 4 m in diameter. The Columbus Free-Flying Laboratory was totally deleted from the Programme. In addition, the adoption of the ISS ESA/NASA Memorandum ofUnderstanding (MOU) meant that only 51% of the technical resources allocated to theAttached Laboratory would be available for European utilisation. Consequently, the above list of facilities studied far exceeded the accommodation now allocated to ESA. They had to be reduced to four microgravity-dedicated facilities, each the size of one International Standard Payload Rack (ISPR), i.e. 1.05 m in width, 2.03 mhigh and 1.01 m deep. The utilisation-preparation part of the Columbus Programmeincluded a European Drawer Rack for small, standardised payloads from various user disciplines, and a European Storage Rack (ESR) and Laboratory SupportEquipment.

The allocation of the technical resources, such as the number of racks, power and heatrejection, crew time, data transmission and upload/download capacity has beenbased on the value of the contributions of the ISS Partners to the overall Space StationProgramme. If the later-added Russian ISS contributions are not taken into account,then the European Columbus contribution represents 8.3% of the ‘western part’ of ISS.NASA is the major ISS Partner with 76.6% of the western part, followed by Japan with12.8%, ESA with 8.3% and Canada with 2.3%.


further research activities in that period. (The MFC Programme, discussed below,covers only facility hardware costs, not research activities). If a budget is not allocatedfor such activities in this interim period, the most important European ISS usercommunity could largely disappear.

4.2.4. The ESA ‘Microgravity Facilities for Columbus’ (MFC) Programme

During the 1980s and the first half of the 1990s, ESA performed design and coststudies of Columbus, the European contribution to the ISS. During this period theAgency’s Member States repeatedly requested reductions in the technical content andfinancial envelope of the Columbus Programme. Finally, in September 1995, when thecorresponding decisions of the other ISS partners, i.e. the USA, Japan and Canada, hadalready been taken, an ESA Council Meeting at Ministerial Level took place to decideon the development of Columbus, and its utilisation preparation and promotion. Atthis time it was planned to utilise the ISS for multi-disciplinary research, applicationsand technology for a period of 15 years after the completion of the Station’s orbitalassembly.

In parallel with the Columbus definition studies, ESA conducted ISS utilisation studiesand issued Preliminary Calls for Experiments. These showed that the major ISSutilisation areas would be research and applications in the fields of life and physicalsciences and applications, and potentially industrial and commercial applications.

In the second half of the 1980s, the European microgravity user community defined(at ESA’s request) a number of multi-user facilities for the Columbus AttachedLaboratory (known until then as the Attached Pressurised Module) and for the

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Columbus Free-Flying Laboratory

– Automated Biolab– Crystallisation Facility– Thermophysical Properties Facility– Central Robotic System for Sample/

Specimen Supply to Facilities – Sample/Specimen Storage Racks– Protein-Crystallisation Facility– Low-Temperature Vapour Crystal

Growth Facility

Columbus Attached Laboratory

– Anthrolab (AL)– Biolab (BL)– Biotechnology Facility (BF)– Fluid-Science Laboratory (FSL)– Combustion Facility (CF)– Low-Temperature Materials

Processing Laboratory (LTMPL)– High-Temperature Materials-

Processing Laboratory– Containerless Processing Laboratory

Figure 4.2.3. ESA annual budgets for the various microgravity programmes

Mill

ion

Euro

s

The four racks selected for development within the framework of a separate‘Microgravity Facilities for Columbus’ (MFC) Programme were the following:– Biolab– Materials-Science Laboratory (MSL)– Fluid-Science Laboratory (FSL)– European Physiology Modules (EPMs).

The scientific and technical aspects of these microgravity multi-user facilities aredescribed in Chapter 5.2. The MFC Programme includes the development of these fourfacilities for the ISS. It also includes a programme element called ‘User Support’,covering the development of standardised experiment containers for Biolab and FSLand cartridges for MSL users. Another programme element called ‘Second-GenerationFacility Studies’ covers design and cost studies for a second generation of microgravityfacilities for ISS. The MFC Programme was approved together with the ColumbusProgramme in September 1995.

The approved financial envelope for the MFC Programme is 202.6 MAU (MEuro) at1995 economic conditions. Only eight ESA Member States contribute to the MFCProgramme: Germany (40.8%), France (23.3%), Italy (16.1%), Belgium (10.2%),Switzerland (4.1%), Spain (2.0%), Denmark (2.0%) and The Netherlands (1.5%). Sincethe detailed design studies (Phase-B) of the MFC elements were still financed by theEMIR-1 Programme, the MFC Programme began with the first hardware developmentin 1997. It is planned that hardware development and qualification of all MFC facilitieswill be concluded by 2003.

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CHAPTER 5 THE FUTURE OF MICROGRAVITY RESEARCH

5.1 Microgravity Experimentation in the Space-Station Era

M. Heppener

5.1.1 Introduction

Research in the life and physical sciences in space began in the late 1950s, with earlyexperiments in drop towers, and progressed in the 1960s with Russian capsules andthe Apollo flights. After the early concerns as to whether humans could even survivespaceflight, the emphasis began to turn towards more fundamental research on theinfluence of gravity on physical and biological processes. Those early experiments ledto enough interesting results and theories to warrant a more concentrated effort.

The survey of the current status of microgravity research, presented in Chapter 2,shows clearly that a solid body of valuable results and a well-based programme of ongoing research now exists. However, the rate of scientific progress in this field hasbeen slow relative to that of comparable terrestrial-based research. This is almostentirely due to the very limited amount of actual experimentation time that has beenavailable in space in the past.

It should be recalled that in the early days of the development of the Space Shuttle, inthe seventies, official NASA expectations were that some 50 flights would take placeannually. In reality, not more than nine Shuttle flights have been realised in any givenyear, largely due to the cost and complexity of flight preparations and operations. Thegreatly increased cost, over that originally presented by NASA, has further restrictedEuropean flight opportunities. In addition, the Challenger accident in 1986 meant notonly a hiatus of about five years, but also led to an important increase in safetyrequirements and, consequently, in the mission preparation time. Although for someexperiments alternative flight solutions could be found, for example by boosting theEuropean effort in sounding rockets, this cannot compare to the scientific return thatcan result from routine long-duration human missions.


programme could consist of possibly several space experiments. These will be centredon the ISS, but may also utilise sounding rockets or unmanned carriers, dependingupon the requirements. They are also likely to be complemented by continuousground-based research. In such an approach, the separation between the research tobe carried out in space and that of the traditional scientific discipline will bediminished. Rather than delivering only one data point after years of preparation, acomprehensive research programme can be expected to yield several publicationsover its lifetime. Such an approach also has the important consequence that it makesresearch in space more compatible with the average duration of normal researchprojects, and also with the typical four-year duration of a PhD.

In order for this future vision to become reality, it is a top priority to make access tospace as simple as possible and to reduce the preparation time and paperwork to aminimum. That will definitely require some learning and adapting from the variousspace agencies involved with ISS operations.

- Application-Oriented Research

In recent years, an additional demand has emerged for easy access to space, which isa result of the onset of application-oriented research. ESA is stimulating thisdevelopment with a specific Microgravity Application Programme (MAP), as discussedin Section 3.3, that has the possibility to support these projects financially. In responseto recent AOs, ESA has received numerous proposals describing projects that arerelevant for society or industry. These have included research projects in the medicalfield, in the casting and petrochemical industry, and in energy production andenvironmentally relevant processes. After rigorous evaluation of the proposals, ESAhas accepted 48 of these projects. Within those accepted, there are some 125European companies participating. In all cases, the funding of these projects can bedescribed as a public-private partnership in which industry, academic institutions andESA each pay roughly an equal share of the total project costs. It is clear that there isa very promising interest by industry in research in space and this needs to be furtherencouraged and nurtured. However, in order to make the ISS a really interestingindustrial research environment, its operations must become compatible with thetypical 1 – 2 year planning cycle that is customary in industrial R&D, and theassociated costs firmly restrained.

- Operational Considerations and Constraints

In the past, almost all space missions were prepared in a ‘batch mode’, i.e. one inwhich planning, testing and training were performed extensively on the groundbeforehand, in order to ensure a flawless performance in space. For manned missions,this meant that the crew’s activities were more or less prescribed from minute tominute.


The International Space Station (ISS) will be a quantum leap in this respect. This will bethe first time that European scientists will have access to a permanently functioningand well-equipped laboratory in space. Consequently, microgravity research willfinally have the opportunity to firmly establish itself as a valid and important scientificendeavour in its own right. The ESA plans to enable this opportunity to be translatedinto reality are outlined in the following discussion of the utilisation of the ISS formicrogravity research.

5.1.2 The ISS: an International Endeavour

From the outset, the ISS has been designed to be an international collaborative projectbetween the partners. For researchers who want to use the ISS, it should really becomea ‘station without walls’. In other words, it should be irrelevant in which module of theISS an experiment is to be performed or who is the formal owner of the facility that isused. In practice, the international partners in the ISS programme are trying toaccomplish this by setting up International Working Groups, to deal with variousaspects of the Station’s utilisation. Three such working groups are presently active: theInternational Strategic Life-Sciences Working Group (ISLSWG), the InternationalMicrogravity Strategic-Planning Group (IMSPG), and the Multilateral ConsultativeWorking Group for Commercial Programmes (MCWG-CP).

The first two groups are particularly active in streamlining and defining thecomplement of available facilities. In addition, they organise the internationalAnnouncements of Opportunity (AOs) for experiments and the subsequent globalexperiment selection process for their respective disciplines. The selection isperformed by international, independent peers who use a set of agreed criteria thatfocus on scientific merit. After the scientific review by the peers, a technical review ofthe feasibility is organised. By this means, it is intended to guarantee that ultimatelythe best international projects will be performed on the ISS.

- Scientific Research

For those scientists with past experience of performing experiments in space, theInternational Space Station will differ markedly from the earlier missions. The ISS is aplatform with a planned lifetime of 15 years. For that reason, its operational scenariois completely different from other manned missions on the Space Shuttle, let aloneunmanned carriers or short-duration flights on sounding rockets. The best comparisonmight be the Russian space station Mir, on which non-Russian experiments were alsoperformed during co-operative, but cost-reimbursable, missions with NASA, ESA andseveral individual countries during the past decade.

Having more regular and routine access to space means that, for the first time,scientists will be able to set up comprehensive research programmes. Such a

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It is expected that already after the first few Increments, a lot of experience will havebeen gathered on the real constraints of ISS experiment planning and operations. Withtime, therefore, the ISS will grow into its role of a flexible, well-equipped, multi-purpose,research laboratory in low Earth orbit.

- Complementarity with Other Research Opportunities

Although the ISS will be the platform of choice for most experiments, there will remaina continuing need for other, complementary research platforms. Ground-basedresearch, as has been said before, is an essential ingredient in most researchprogrammes. The use of facilities that simulate microgravity to different degrees, suchas clinostats, random-positioning machines, free-fall machines, together with the useof hyper-gravity centrifuges, will be of interest, since they can be used to help tailorand optimise the experimental conditions of the space experiment.

Parabolic flights will continue to be used as a very useful, low-cost preparatoryresearch facility. Drop towers and especially sounding-rocket flights provide additional,very flexible research platforms, which can be used for complete scientific studies,provided that the phenomena occur fast enough. Sounding rockets, together withunmanned retrievable capsules such as the Russian Foton, have undeniableadvantages over human missions in that they demand much lower safety standardsand are therefore amenable to experiments with more hazardous materials. Thenthere is the Shuttle, which can provide rapid access to astronauts to obtain biomedicalsamples directly after the onset of microgravity, which for some studies is essential.

The ISS, on the other hand, offers long-duration microgravity access to a large numberof test subjects, advanced facilities and in-orbit analysis facilities. It will also allow forexperiment repeats with different parameters, when a first run does not yield theexpected results. This will make research on the ISS more comparable to the normalpractices used in terrestrial laboratories.

In summary, ESA intends to continue to provide research projects with various typesof flight opportunities, tailored to specific schedules and needs.

- The First Experiments on the ISS

In recent years, ESA has issued AOs in which the ISS facilities have also been offered.As a result, there now exists a list of approved experiments that will be performedinitially on the Space Station. In the period before the Columbus Laboratory islaunched, these experiments will be executed under agreements with NASA for the so-called ‘Early Utilisation of the ISS’. More details of these arrangements are given inSection 5.2.2


For the Space Station, the operational scenario will be different. The basic planningunit is called an ‘Increment’ (Fig.1.8), each of which covers approximately threemonths. It begins as a new crew arrives at the Space Station and new experiment-specific equipment, such as samples, consumables and inserts for the MFC and EDRfacilities, are delivered, together with software updates for all equipment. Thepreparations for each Increment form a step-wise process, which starts approximatelytwo years earlier. During this period, the requirements of the different payloads will bematched up and a complete simulation of the activities to be conducted during theIncrement will be performed, in order to identify potential incompatibilities. At thistime also, a complete overview will be made of the resource requirements during theIncrement. Some of these resources, in particular the up- and down-loads, are ratherscarce. Indeed, they may well be the limiting factors that determine the total numberof experiments that can be performed within each Increment.

In Europe, an important role is given to the various User Support and OperationCentres (USOCs), located in different participating ESA Member States. It is here thatthe direct contact with the experiment team is established. The communications withthe ISS will also be made through the USOCs, since they are connected into the ISSground infrastructure. A selected USOC has responsibility for one of the Europeanfacilities that is on-board the ISS. Each USOC maintains the technical and scientificknowledge necessary to operate its designated facility.

Once in orbit, experiments will be performed in the various facilities that are availablein that particular Increment. Remote operation of the payloads and ‘telescience’,which allows the Earth-based scientist to oversee and control the experiment inprogress, will be applied.

The resources set aside for experimentation are accommodated within the overallresources, the main part of which actually goes into the operation of the Space Stationitself. It is to be expected that during a mission Increment, unforeseen events mayarise that will require adaptation of the planning.

The above brief outline of the operational aspects of experimentation on the ISSreveals that there are certain conditions that have to be met in order to enhance itsscientific output. These include:– Reducing experiment preparation time and flight costs. Special ‘fast-track’ access

possibilities need to be created.– Specific attention should be given to in-orbit sample preparation and analysis.– Increment planning should allow sufficient flexibility to absorb unforeseen events

without necessarily sacrificing experiments.– Maximising the amount of resources that can be made available to experiments

must be the top priority in the planning process.

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- Future Outlook

In response to several AOs in the past, a large number of experiments have beenproposed. These have been analysed and subjected to peer group review.

As explained earlier, ESA is stimulating specifically application-oriented research. This isdone especially within the framework of the Microgravity Application Promotion (MAP)programme. A list of the presently approved MAP Projects, with some details abouttheir objectives and future implementation, is given in the Appendix (Chapter 6.8)

Although European facilities and experiments will be flown during the build-up phaseof the ISS, the major European utilisation of the Space Station will only start when theColumbus Laboratory is in orbit. At that point, the four ESA Microgravity Facilities forColumbus, namely the Biolab, Fluid-Science Laboratory (FSL), the second Material-ScienceLaboratory (MSL-2) and the European Physiology Modules (EPMs), will also beavailable. In addition, a fifth facility, the European Drawer Rack (EDR), will be available tooffer flexible accommodation for smaller payloads that can be exchanged at eachIncrement.

Since the launch of the Columbus Laboratory is now expected only in late 2004, nospecific selection of experiments for those facilities has yet been made. However,several proposals received in response to recent AOs, dealing with both basic andapplication-oriented research, have asked for the development of new facilities orspecific upgrades to existing ones. To give an impression of what can be expected inthe future, a few examples will be described below.

Measurement of Thermo-physical PropertiesKnowledge of the thermo-physical properties of molten metals is not only of interestfrom a purely scientific point of view, but also has many practical implications. For themodelling of processes in the casting industry, for example, these data essentiallydetermine the accuracy that can be obtained, and thereby the precision with whichthese processes can be finely adjusted to maximum effectiveness. Clearly, this is atopic of significant economic impact.

However, it is not easy to measure these parameters. The reason is that many metalsonly reach their molten state at such elevated temperatures (1500°C or higher) thatthe material of the crucible in which the sample is held starts to dissolve into themetal, thereby invalidating the measurement. By performing these measurements inspace, samples can be heated and processed without a crucible by containing them inan electromagnetic field. In this way, the thermo-physical properties of pure metalscan be studied, and in addition very detailed solidification experiments on under-cooled melts can be performed.


The facilities that are planned to fly in this time frame are the Advanced Protein-Crystallisation Facility (APCF), the European Modular Cultivation System (EMCS), theMatroshka experiment, the Expose facility and the first version of the Material- ScienceLaboratory (MSL).

The first of these to be delivered to the ISS will be the APCF (reflight; see Table 6.2),presently foreseen for a launch in 2001. The nine experiments planned for this facilityare expected to benefit from the much longer time available on the ISS for growing thelarge-sized protein crystals that are required for X-ray diffraction experiments tounravel their molecular structure.

The European Modular Cultivation System (EMCS) will be launched to the ISS in 2003.The six EMCS experiments presently selected (including two from the USA) are designedto study the effect of gravity and radiation on plants, algae and simple organisms.

Matroshka and Expose will be housed at external locations on the ISS. Matroshka is ahuman ‘phantom’ model, which will be placed on the outside of the Russian Zvezdamodule, in 2003. It is intended to allow the radiation doses received at differentlocations in the human body to be quantified. Expose will be launched in 2004 andwill be used for exobiology experiments that study the effects of space conditions(vacuum, radiation, etc.) on spores and other biological substances. Presently, eightexperiments from multi-national teams are foreseen.

The first Material-Science Laboratory (MSL-1) will be launched in 2003. The MSLFurnace Facility will have two European and two American exchangeable furnaceinserts. Nine experiments have been selected at the present time. They are intended tostudy both fundamental and application-oriented themes in the solidification ofmetals and alloys and crystallisation of semiconductors.

In addition to these experiments that are to be performed in ESA facilities, ten ESAexperiments in the area of human physiology have been selected for flight during thefirst years of ISS utilisation. They will be performed in the NASA Human ResearchFacility (HRF). In co-operating with NASA on the HRF, ESA is contributing the MuscleAtrophy Research and Exercise System (MARES), the Percutaneous Electrical MuscleStimulator (PEMS), the Hand-Grip Dynamometer (HGD), and a major part of thePulmonary Function System. These experiments will focus on the effects of gravity onthe human body, in particular the cardiovascular system, sensorimotor co-ordinationand the muscle system. The findings of these studies are important for the health andfunctioning of astronauts, but are also very relevant to the understanding of humanhealth problems and diseases on Earth.

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Equipment for Treating Physiological De-conditioning It is a well-established fact that astronauts in space experience physiological de-conditioning effects that closely resemble health problems on Earth related to ageing,immobility or disease. Examples are bone mass loss, muscle atrophy, and effects onthe cardiovascular, equilibrium and breathing systems. A great number of experimentproposals address these issues. Specific equipment is proposed to arrive at moreadvanced diagnostic techniques and also to find adequate physical countermeasures.

Presently under development or study are: a portable gas analyser to check lung function,a portable device that monitors several cardiovascular parameters simultaneously,advanced diagnostics of bone structure, and an exercise machine that has proven inpreliminary studies to be very effective against these de-conditioning effects.

Since there is clearly a close link between research in space and the eventual clinicalapplication, these proposals are co-ordinated by teams comprising medical doctorsand medical companies. Chapter 2.1 gives more information on the subject of spacemedical research.

Other Equipment StudiesAdditional studies are being performed on possible inserts for the EDR, FSL or MSL.The present list includes:– a facility to study interactions in cosmic and atmospheric particle systems – a microgravity plasma facility– a facility for thermal-transport phenomena in magnetic fluids– a facility for diffusion and Soret coefficient measurements– an insert for space combustion research (for inclusion in the NASA Combustion

Facility) – a facility for the study of emulsions– an insert to study geophysical flows – a small-rodent research facility – a facility to study life-support systems.

It is to be expected that even more studies will be initiated following futureAnnouncements of Opportunity. Of course, this does not imply that all of these studieswill eventually lead to development and flight. However, it is already evident that theISS and its facilities will allow for the flexible accommodation of the research needs ofthe user community both now and in the future.


Following the receipt of several very-high-quality proposals from teams that include alarge number of industrial companies, ESA is now studying the development of anelectromagnetic levitation furnace for the Material-Science Laboratory, namely MSL-EML. A more detailed discussion of this topic can be found in Sections 2.3.2. and 5.2.2.

Three-Dimensional Tissue CulturingA major activity in present-day biotechnology is the study of methods to developartificial human tissue and organs. Unfortunately, attempts to grow functional tissuesfrom human cells on Earth are limited by the fact that the cells tend to grow only intwo dimensions. Therefore, experiments in space have been proposed to study thespecific conditions that are important for cellular growth in three dimensions in theabsence of gravity. As a first step, an attempt will be made to grow artificial cartilage.If successful, the technique can be extended to determine the specific growthconditions needed for more complex tissue.

Over the past two decades, many experiments have been performed on mammaliancells in space, and therefore the technology needed to grow these cells in space is nowwell-developed. The next step is to develop a specific Bioreactor for Mammalian TissueCulture (BMTC). For this, again based on a proposal with some medical companiesinvolved, a study is now being performed. It is the intention that a future BMTC will bedeveloped to be compatible with the European Drawer Rack. More information on thesubject of tissue engineering is given in Section 3.2.15.

FoamsUnder terrestrial conditions, foams can form as an unwanted by-product in chemicalreactions, or as a specifically desired end-result. Both cases are interesting from atheoretical and a practical point of view. The study of foams on Earth is influenced bythe fact that the drainage of liquid through foam takes place under the influence ofgravity, which creates a natural gradient in wall thickness. In certain cases, this can bea handicap when measuring foam properties. In addition, solidified foam made ofmolten metal can be a very interesting new material whose properties will be afunction of wall thickness. A more detailed discussion of foam physics can be found inSection 2.3.5.

Two MAP proposals, submitted by teams comprising leading industries and specialistuniversity researchers, therefore aim to study foams directly in a space environment.For the foams based on water or organic solvents, a special insert for the Fluid-ScienceLaboratory is being studied. For foams made of liquid metal, the intention is to developan insert for the Material-Science Laboratory or the European Drawer Rack.

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As mentioned in Section 5.1, prior to the launch of the Columbus Laboratory, anumber of other ESA-selected early European experiments/facilities will beaccommodated on the ISS, either in the US Laboratory as from 2001 or on the externalviewing platforms.

- ESA Research Facilities in the US Laboratory

The facilities to be located in the US Laboratory are in most cases follow-ondevelopments of EMIR-1 equipment, such as the Muscle Atrophy Research andExercise System (MARES), PEMS-2 (a muscle stimulator device), a Hand-Grip and Pinch-Force Dynamometer (HGD-PFD) and the European Modular Cultivation System (EMCS)for plant research. All of these life-sciences facilities will be described briefly below.

In addition, the first facility of the Materials-Science Laboratory (MSL), including theESA Solidification and Quenching Furnace (SQF) and the Low-Gradient Furnace(LGF) as inserts, will be accommodated for two years in this US Laboratory.

- ESA Payloads on the External Platform of the ISS

These will include payloads from the fields of space science (payloads ‘Solar’ and‘Sport’), Earth Observation (planned payload: Focus, an intelligent Fire Detection andCharacterisation Infrared Sensor System) and Technology (payload: EUTEF, a EuropeanTechnology Exposure Facility). There will also be two payloads that have been selectedby ESA for external accommodation, from the areas of life sciences and physicalsciences. These are:– Expose, a Sun-pointing exposure platform for exobiology experiments – ACES, a microgravity ‘Atomic Clock Ensemble in Space’ payload, the core of which

is a laser-cooled caesium atomic clock.

Both Expose and ACES are briefly described below.

- European Payloads in the Columbus Laboratory

By far the most important of the ESA contributions for the utilisation of the ISS byEuropean scientists are the Microgravity Facilities for Columbus (MFC), i.e. Biolab, theFluid-Science Laboratory, the European Physiology Modules (EPMs), and the Material-Science Laboratory (MSL). The second MSL facility, an Electro-Magnetic Levitationheating facility (MSL-EML), will be accommodated in the Columbus Laboratory.

In addition to the MFC laboratories, the European Drawer Rack (EDR) is also plannedto be permanently accommodated in the Columbus Laboratory. It provides theinfrastructure for four standardised experiment drawers and four standardised ISSlockers (MDLs). Both can be exchanged in orbit. The EDR is not dedicated to a specific


5.2 Major ESA Microgravity Facilities for the ISS

G. Seibert

5.2.1 Introduction

At the end of 1998, the first two elements of the International Space Station, ‘Zarya’and ‘Unity’, were launched and subsequently joined together in space. The third ISSelement, the Russian service module ‘Zvezda’ (star), was launched on 12 July 2000and later docked with the Zarya-Unity complex. Zvezda not only provides for the firsthuman habitation of the ISS, but it also accommodates the two Europeanexperiments:– the Global Transmission System (GTS), which broadcasts accurate timing and data

signals to multiple users on Earth, and– a German Plasma Krystall Experiment (PKE, see Section 2.3.8).

Furthermore, within the framework of a bi-lateral agreement between the RussianSpace Agency and ESA, the ‘Matroshka’ radiation experiment will be accommodatedon Zvezda in the early-2003 time frame.

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Figure 5.2.1. (a) The cargo unit ‘Zarya’, thefirst element of the International SpaceStation (ISS), mated with the ‘Unity’connecting module (courtesy of NASA)(b) The ESA Columbus Laboratory for the ISS

(a)

(b)

5.2.2 ESA Microgravity Facilities in the Columbus Laboratory

The programmatic aspects of the ESA Microgravity Facilities for Columbus (MFC)Programme approved in 1995 are described in Section 4.2.4. The major experimentalfacilities being developed within that MFC programme for accommodation in theSpace Station are discussed here, together with the characteristics of the Protein-Crystallisation Diagnostics Facility (part of the EMIR-2 Programme).


discipline. It offers a quick turnaround and thereby increased flight opportunities forthe microgravity user community. A typical EDR payload, the ESA Protein-Crystallisation Diagnostics Facility (PCDF), is described below.

Table 5.2.1 provides a summary of the main European facilities to be provided for the ISS, their locations, start of operations, and the main areas of research for eachfacility.

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Table 5.2.1 European Life- and Physical-Sciences Facilities on the ISS

Experiment Research Area Location Ops. Funding CommentsFacilities on ISS Begin Programme

Biolab Cell and developmental Columbus 2005 MFC Microgravity Facilities forbiology, biotechnology Laboratory Columbus (MFC)

Fluid-Science Fluid dynamics, capillarity, Columbus 2005 MFCLab. (FPM) phase transitions, critical- Laboratory

point phenomena, bubblephysics

Materials- Solidification physics, Columbus 2005 MFC Furnace inserts: 2 from ESA,Science Lab.-1 diffusion, crystal growth Laboratory 2 from NASA, 1 from DLR(MSL-1)

Materials- Electro-Magnetic Levitation Columbus 2006 MFC An ESA–DLR co-operation,Science Lab.-2 Furnace, to study nucleation, Laboratory & DLR MSL-2 will be the first(MSL-2) metastable phases, thermo- exchange of a large

physics properties Columbus facility

European Human physiology, muscles, Columbus 2005 MFC Modules are supplied by ESA,Physiology bone, cardiovascular, Laboratory Germany, Denmark, FranceModules neurology, vestibular, fluid and Italy(EPMs) regulation

Protein-Crystal. Study of nucleation and Columbus 2005 EMIR-2 The PCDF is the first payloadDiagnostic growth of protein crystals, Laboratory located in theFacility (PCDF) using various optical European Drawer Rack

diagnostic systems

European Accommodates sequentially, Columbus 2005 Columbus Payload from EMIR-2 Prog.Drawer Rack life- and physical-sciences Laboratory Utilisation and future life/physical-sci.(EDR) payloads, e.g. the PCDF, and appl. programmes

MTCS, MAPs, etc.

Biotechnol. Cell and tissue growth Columbus 2006 Future life- European Drawer RackMammalian and differentiation Laboratory sci. and payload for tissue Tissue Cult. phys. sci. engineeringFacility (BTMC) programmes

European Mod. Multi-generation studies in US 2003 EMIR-2 Containers are larger than inCultiv. System plants and fungi, and the Laboratory Biolab, to facilitate growth(EMCS) study of gravity perception studies

/......

Table 5.2.1 European Life- and Physical-Sciences Facilities on the ISS (cont’d)...

Experiment Research Area Location Ops. Funding CommentsFacilities on ISS Begin Programme

Photoacoustic The PAM and PFM are part US 2002 MFC The Pulmonary FunctionAnalyser Module of the Pulmonary Function Laboratory System will be (PAM) accommodated in the NASA

Human Research Facility

Pulmonary- The Pulmonary Function US 2002 MFCFunction Module System was developed in Laboratory(PFM) co-operation with NASA for

studies of lung andcardiovascular behaviour

Muscle Atrophy Muscle, skeletal and US 2002 EMIR-2 An ESA contribution to theRes. and Exercise biomechanical studies Laboratory NASA Human ResearchSyst. (MARES) Facility

Percut. Elec. Neuro-muscular research, in US 2002 EMIR-2 An ESA contribution to theMuscle Stimulator association with the Muscle Laboratory NASA Human Research(PEMS) Atrophy Research System Facility

Handgrip & Muscle atrophy in the hand US 2001 EMIR-2 Used also in NASA’s crewPinch-Force and fingers. Stressor for the Laboratory health-care systemDynamometers cardiovascular system

‘Matroshka’ Space-radiation depth-dose Exterior 2003 EMIR-2 Simulation of human tissuemeasurement in human of Zvezdamodel

Atomic Clock ACES is a laser-cooled ISS External 2004 Columbus ESA-CNES co-operationEnsemble in caesium clock, with an Platform or Utilisation Switzerland provides Space (ACES) H-maser reference clock Columbus and CNES H-maser clock. GPS

Platform improvement in microgravity

‘Expose’ Exobiology. Effects of the ISS External 2004 EMIR-2 Survival of organisms inspace environment on Platform or interplanetary spaceorganisms Columbus

Platform

position would be used for a European Drawer Rack (EDR). This was designed for theaccommodation of smaller, quick-turnaround experiments. The fifth ISPR was plannedas a European Stowage Rack (ESR), for the storage of experiment containers,samples/specimens and payload-support equipment.

This arrangement was only acceptable because ESA had negotiated with NASA thatthe first ESA Materials-Science Laboratory (MSL-1) would be accommodated for twoyears in the NASA Materials-Science Research Rack (MSRR-1) in the US Laboratory ofthe ISS. That provided earlier access to space experimentation for the Europeanmaterials scientists, since the MSRR-1 comes into operation some two years before thelaunch of Columbus. It also reduced the pressure on accommodation in the ColumbusLaboratory. Under this agreement, NASA would bear the transportation andoperations costs, in return for a 50% NASA usage of this first element of the plannedESA MSL. In addition, this preliminary ESA/NASA agreement allowed access forEuropean Principal Investigators to the NASA-developed furnaces, i.e. within the 50%technical resources allocated to the ESA MSL for ESA usage.

Regarding the distribution of facility-development tasks, it was decided that the mainscientific facilities, the Biolab, FSL, EPM and MSL (consisting of two furnace facilities)would be part of the Microgravity Facilities for Columbus Programme, whereas thedevelopment of the European Drawer Rack and the European Storage Rack would becovered by the utilisation-preparation part of the Columbus Programme.

The four facilities designed and built under the Microgravity Facilities for Columbus(MFC) Programme are:

- Biolab

The technical configuration of the Biolab, intended to carry out research infundamental and applied biology, is based upon the pioneering experimentsperformed by European and US scientists using the ESA Biorack on Spacelab (and lateron Spacehab). It has been elaborated in consultation with the relevant sciencecommunity (Facility Science Team) and within the framework of pre-Phase-A andPhase-A design studies in industry. Taking into account the low level of crew time thatwas to be available on the ISS for payload operations, the Biolab had to operate in ahighly automated mode, despite the fact that automated facilities have very muchhigher development costs. The compromise concept found for Biolab was that itwould operate automatically only after manual loading of the biological specimens,such as small plants, cell cultures, micro-organisms, insects, and small aquaticsystems. Also, the operations within the Bioglovebox are to be performed manually.

In the presently developed Biolab, the biological specimens will be contained instandard experiment containers, which can be accommodated in the incubator on a


In the early 1990s, the MFC Programme, as then proposed, comprised a large numberof facilities, consistent with the technical envelope for Columbus as it existed at thattime. It consisted still of a 12.8 m-long pressurised laboratory, originally called theAPM (Attached Pressurised Laboratory, later renamed the Columbus Orbital Facility(COF), and today called the Columbus Laboratory). In addition there was the ColumbusMan-Tended Free-Flyer (MTFF).

The ESA Member States eventually demanded that the cost of the Columbusdevelopment programme – and with it also the cost of European participation in theISS exploitation phase (planned to last for 15 years after the completion of ISSassembly) – be substantially reduced. Consequently, plans for the MTFF werecancelled and the Columbus Laboratory reduced to half of its original design length,i.e. from 12.8 to 6.4 m. In addition, the NASA/ESA ISS Memorandum of Understandingdetermined that only 51% of the outfitting and use of the Columbus Laboratory wasto be allocated to Europe, an agreement that was in line with the value of the Europeancontribution to the ISS. This corresponds to 8.3% of the ‘western’ part of the ISS, or5.6% of the overall ISS.

A further modification to the ESA Columbus Programme’s content was the inclusion ofa Robotic Arm and of the Automated Transfer Vehicle (to be launched about once peryear by an Ariane-5). This further contribution was introduced in order for ESA toparticipate in the ISS logistic activities. A further important objective of this move was toprovide what is principally a hardware contribution to the ISS exploitation phase, therebyminimising or totally avoiding European cash payments to NASA during that phase.

This major reduction in the size of the ESA laboratory and the allocation of almost halfof the effective volume to NASA meant that only five International Standard PayloadRacks (ISPRs) would be available for European utilisation in the Columbus Laboratory,after allowing for the racks needed for system requirements. Of these five racks, atleast one was needed for storage.

Lengthy discussions ensued with the European microgravity user community on thefull implications of this drastically reduced utilisation capability. There was clearly aminimum need for four multi-user facilities, in order to cater for the four majormicrogravity disciplines of biology, human physiology, fluid physics and materialsscience. The real problems, however, lay in the details of the types of equipment thatshould go into each of these four facilities, and the timetable for their deployment.Eventually, the following recommendation regarding the initial outfitting of theColumbus Laboratory and the technical content of the MFC Programme was agreedupon:Of the five ISPR racks (four lateral, one on the ceiling) available for Europe in theColumbus Laboratory, three were to be used for the Biolab, the Fluid-ScienceLaboratory (FSL) and the European Physiology Modules (EPMs). The remaining

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turbulent flows generated by forces other than gravity, such as surface tension. Theabsence of fluid static pressure, together with the lack of gravity-driven convection,provides optimal conditions for the investigation of capillarity phenomena, phasetransitions and critical-point phenomena. The investigations include condensationstudies and bubble formation, growth and motion experiments.

In order to continue and to extend this type of research, the fluid-science communityrequested the development of a Fluid-Science Laboratory (FSL) for the Space-Stationera. In the past, such research had been supported by the Spacelab multi-userfacilities, known as the Advanced Fluid-Physics Module (AFPM) and the Bubble, Dropand Particle Unit (BDPU).

Following the establishment of the scientific priorities recommended by ESA’sMicrogravity Advisory Committee, the technical requirements for the FSL were definedby a Facility Science Team. They were elaborated in pre-Phase-A and Phase-A studiesin industry, which finally led to the current FSL hardware-development phase.

The FSL consists of a core Central Experiment Module, into which the experimentcontainers are sequentially inserted and operated, together with an OpticalDiagnostics Module (ODM). All functional subsystems are accommodated aroundthese two core elements.


1g centrifuge (there are two of these in Biolab). Both 1g centrifuges are installed in theincubator to enable simultaneous operation in microgravity (i.e. one centrifuge notrunning) and under 1g conditions. This allows the same experiment to be performedsimultaneously in 1g and in microgravity conditions, under identical environmentalconditions in other respects, for comparison purposes.

An Experiment Preparation Unit installed in the Bioglovebox enables controlledthawing of those specimens transported into orbit in a frozen state. Biolab’s majordiagnostic instruments are a microscope and a spectrophotometer, to which thebiological specimens are moved with the help of a handling mechanism. A telesciencecapability allows the Principal Investigators on the ground to follow and interact withthe diagnostic operations. The Bioglovebox, a follow-on development of the Biorack’sglovebox, provides for both further diagnostic work and also manual liquid-handlingand fixation. There are two cooler systems for specimen preservation. There is also thepossibility to store the biological specimens in a separate – 80°C freezer (called MELFI)using small vials. These are manually transported between MELFI and Biolab.

- Fluid-Science Laboratory (FSL)

Studies in fluid dynamics under microgravity conditions have provided an importantmeans for testing the theories that describe three-dimensional laminar, oscillatory and

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Figure 5.2.2. The ESA ‘Biolab’ multi-user facility for biological research. The loading ofsamples and operations in the Bioglovebox are conducted by a crew member. Thereafter,the experiments are performed automatically, with the possibility of remote guidance/intervention from a ground-based scientist

Microscope

Microscope

ESA/D. Ducros

Microscope

Spectrophotometer Video Recorder

Laptop Computer

Bioglovebox

Incubator(+18...+40ºC)with 2 centrifuges(0.001g...2.0g)and Life Support System(02, CO2, humidity,ethylene removal)

Temperature Controlled Unit 1(–20...+10ºC)

Temperature Controlled Unit 2(–20...+10ºC)

Front Mounted Camera

EC Utility Lines

Stowage Container 2orUpgrade Volume

Stowage Container 1

Video Management Unit(VMU)

Master Control Unit(MCU)

Work Bench Drawer

Laptop Unit (LTU)

Power Cotrol Unit(PCU)

Second Water Loop Assembly(SWLA)

Avionics Air Assembly

Optical DiagnosticsModule (ODM)

Central ExperimentModule (CEM2)

Central ExperimentModule (CEM1)

Figure 5.2.3. The ESA Fluid-Science Laboratory, to be located in the Columbus Laboratory

coordinated operation. These Modules are accommodated in two types of standard-rack container.

Based upon the recommendations of the EPM Facility Science Team, the initial EPMconfiguration consists of the following Science Modules:

– Multi-Electrode EEG Measurement Module (MEEMM)This module provides facilities for non-invasive research into brain functions. Up to128 electrodes can be placed on the subject’s head and various stimuli andstressors (e.g. muscle stimulators) introduced. In combination with another sciencemodule, the Elite-S2, simultaneous measurements of body movements and brainactivity can be performed. The MEEMM will also take measurements during sleepor other bodily activities.

– Elite-S2This science module is an ASI/CNES contribution. It is a follow-on development ofthe Elite equipment originally developed by ASI for experiments on Mir and of theKinelite equipment developed by CNES for experiments on the Space Shuttle. Itenables quantitative analysis of human kinematics in microgravity, by applying fourcameras for 3D-photogrammatic measurements of crew movements.


The ODM’s optical diagnostic equipment provides for:– visual observation (photographic and electronic imaging) in two axes, with a

variety of illumination options– interferometry in two axes by convertible interferometers, such as holographic-,

Wollaston/shearing-, speckle pattern interferometers and a Schlieren modecombined with shearing

– infrared thermographic mapping of free surfaces– particle image velocimetry.

For each experiment category, dedicated Experiment Containers will be developed,with standardised interfaces. These containers are inserted manually by the crew intothe Central Experiment Module. They accommodate the experimental fluid andadditional experiment specific diagnostics. The FSL has a full telescience capability,which allows the operating mode to be changed from the ground (in addition to thepossibility of interaction by the flight crew). However, fully automatic experimentprocessing is planned to be the routine operating mode.

- European Physiology Modules (EPMs)

The scientific priorities in the field of human physiology for the Space-Station era weredefined by the ESA Microgravity Advisory Committee/Life-Sciences Working Group in1994. They included research topics such as bone remodelling and demineralisation,muscle degradation, blood pressure and volume regulation, blood components andfluid/electrolyte regulation, lung ventilation and perfusion and the human sensoryand balance system.

During the Spacelab era, human-physiology research was performed with the help ofthe large multi-user facilities Anthrorack, Sled, and the Torque Velocity Dynamometer,together with the experiment-specific equipment. In the context of ESA’s Euromirmission and the Mir missions of certain ESA Member States, a number of physiologysubdiscipline-dedicated instruments were developed. ESA developed a BoneDensitometer and a second-generation Respiratory Monitoring System. ESA’s MemberStates developed Medex (DLR) and Physiolab (CNES) for cardiovascular research, andElite (ASI) and Kinelite (CNES) for the quantitative analysis of human kinematics inmicrogravity.

After taking account of the scientific priorities established by the advisory groups andthe past results of space human-physiology experiments, the ESA EPM Facility ScienceTeam defined the EPM’s technical content.

Contrary to the technical layout of the other MFC facilities, the EPM is not a single largemulti-user facility. Rather, it is composed of a number (up to nine) of exchangeableScience Modules (SMs), plus the facility infrastructure needed to support their

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Sample Collection Container

Utility DistributionPanels

Bone AnalysesModule

MEEMM

ELITE-S2(ASI/CNES)

Cardiolab (CNES/DLR)

NASA Module

Power Distribution Unit

Figure 5.2.4. The European Physiology Modules, to be located in the ESA ColumbusLaboratory. The NASA Human Research Facility will be co-located there to allow combinedexperimentation

A Science Team addressing materials-science furnaces for the ISS had initially definedthe following seven furnaces, for which design and cost studies (Phase-A) wereperformed by industry:– High-Precision Furnace HPF– Solidification and Quenching Furnace SQF– Materials-Processing Furnace MPF– Bridgman High-Temperature Furnace BHF– Gradient-Freeze Furnace GFF– Zone-Melting Furnace ZMF– Floating-Zone Facility FZF.

The Science Team concluded, following a special Workshop, that the Gradient-FreezeFurnace should have the highest priority. However, this was recommended oncondition that European materials scientists would be allowed to utilise the otherfurnace types that were to be developed by NASA and the Japanese space authorities.Unfortunately, such a commitment could not be obtained from NASA and theJapanese Space Agency at that time. Furthermore, the industrial study of the GFFshowed that it resulted in the highest risk in terms of meeting the very exactingtechnical requirements set for it. The Science Team therefore agreed to thecompromise of two furnace inserts (SQF and LGF), but a single furnace infrastructure,and the option of further insert developments by national space authorities. Also,NASA had a preference for the Solidification and Quenching Furnace.

The MSL Science Team defined the stimuli/diagnostics measurements for the SQF asfollows:– measurement of supercooling by the Seebeck effect– phase-boundary demarcation by the Peltier effect– solidification-front position and planarity to be evaluated by an ultrasound device– various temperature measurements.


– Xenon Skin Blood-Flow Measurement Instrument and Physiological-PressureMeasurement InstrumentThese two instruments, contributed by the Danish space authorities, will be used tomeasure skin blood flow and physiological pressures, such as the central venousand oesophageal pressures.

– CardiolabThe Cardiolab is a follow-on development of the French Physiolab and the German Medex. A joint contribution by CNES/DLR, it comprises various equipment elementsto support cardiovascular research and the health of astronauts on short- and long-term flights, and it provides the means for operational medicine/prevention anddiagnostics. The research objectives are fluid-volume regulation, haemodynamicsand surveillance of the main organs in the thorax/abdominal region.

– Bone-Analysis Module (BAM)The BAM enables an evaluation of the efficiency of countermeasures against bonedemineralisation, bone loss and deterioration in microgravity to be carried out. It isderived from the Bone Densitometer developed for and flown by ESA on theEuromir ’95 mission. It measures ultrasound transmission delays and broadbandultrasound attenuation in weight-bearing bones.

– Sample-Collection KitThis is similar to the blood, urine and saliva kits flown on the Euromir missions. Itallows the collection of samples of body fluids in a controlled environment, for latertransport to the ground for analysis. The kit includes waste-management utilities forthe disposal of bio-hazards or sharp items.

- Materials-Science Laboratory (MSL)

As already explained in the Introduction (Section 5.2.1), the first of the two MSLfacilities, with associated infrastructure, will initially be accommodated for two yearsin NASA’s US Laboratory, from 2003. Thereafter, it will be located in the ColumbusLaboratory.

This first MSL facility will be able to accommodate:– the ESA Solidification and Quenching Furnace (SQF) – the ESA Low-Gradient Furnace (LGF)– the NASA Quench-Module Insert (QMI) and Diffusion-Module Insert (DMI).

The decision to develop the SQF and the LGF within the framework of the MFCProgramme was based upon the recommendation of the European material-sciencecommunity and the results of the seven Phase-A studies that were performed with thehelp of European industry.

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Figure 5.2.5. The ESASolidification and QuenchingFurnace and Low-GradientFurnace, which are the firsttwo components of the ESAMaterials-Science Laboratory Furnace Module

Insert(s)

MSL Experiment Module

A more fundamental objective of experimentation with the MSL-EML is the generalstudy of metastable states and phases, mainly:– under-cooling, nucleation kinetics and non-equilibrium solidification– nucleation and growth of metastable crystalline phases

The use of electromagnetic levitation in the terrestrial laboratory is limited because ofthe high levitation fields needed to counteract the gravity fields. On Earth, this type oflevitation requires high power absorption by the sample, which is accompanied bystrong heating. This limits its application to high melting alloys and refractory metals.In space, the positioning forces to compensate disturbing accelerations are aboutthree orders of magnitude smaller. This enables the performance in space of newclasses of experiments that involve slow under-cooling without heterogenousnucleation. On Earth, it is necessary to use very rapid cooling (quenching) in order tobypass the undesired heterogeneous nucleation kinetically. This quenching alternativeis not, however, suitable for the production of bulk material in a metastable state.

The MSL-EML facility, presently under co-operative ESA-DLR Phase-A/B study, islargely based upon the MSL-SFQ/LGF for all supporting functions (power, datahandling, etc). The main difference is that the SQF and LGF inserts are replaced by theEML system, with its dedicated electronics and video system.

The samples to be processed are contained in exchangeable experiment containers,i.e. each container magazine groups together 15 samples with comparable propertiesand process requirements. During processing, the samples can be viewed via thevideo system. The MSL-EML rack also houses the peripheral infrastructure elements,such as pyrometers, vacuum pumps and cooling modules.

Levitation of the samples is performed in oscillating magnetic fields that produce eddycurrents within the samples. In MSL-EML (as in Tempus), a quadrupole field forpositioning and a dipole field for heating are superimposed in a coil system. Sampletemperatures and solidification speeds are measured by three-colour pyrometry.Video cameras control the positioning and permit the measurement of surface tensionand viscosity from the sample oscillations. In the Phase-A/B study of MSL-EML, DLRis concentrating (via a contract with the industrial developers of the Tempus facility)on the design and breadboarding of the automatic experiment-exchange chamber.

- European Drawer Rack (EDR)

In addition to the four main facilities described above, ESA will be outfitting theColumbus Laboratory with a rack designed principally for stowage, together with aDrawer Rack. The latter is designed to accommodate three standard experimentdrawers (8 panel units, 73 litres, 48 kg net user mass) and four standardised Shuttle-type (57 litres, 28 kg net user mass) ISS lockers, all of which can be exchanged whilst


In addition, the furnace should move and the cartridge should be fixed. Thedisplacement rate was selectable over four orders of magnitude. Also, anaccelerometer to be accommodated near to the furnace was requested.

The major characteristics for the Low-Gradient Furnace (LGF) were defined as theshort-term temperature stability (±0.01 K) and the drift. The stimuli and diagnosticrequirements were similar to those of the SQF. Furthermore, a rotating magnetic field,variable in strength up to about 20 mTesla, was made a performance requirement forthe LGF.

In addition to these two furnace inserts, which form the first element of the Materials-Science Laboratory, a further insert is under development by DLR, namely a floating-zone furnace with a rotating magnetic field.

The SQF is optimised for solidification experiments requiring large thermal gradientsand fast sample quenching. The latter is realised by coupling the experiment cartridgevia a liquid-metal sleeve to the water-cooled zone of the furnace. The LGF is optimisedfor crystal-growth experiments using the Bridgman technique.

The SQF and the LGF will operate at temperatures of up to 1550°C. The requiredtemperature stability and uniformity of heating for these two furnaces are at the limitof the associated technology. The diagnostics (Seebeck voltage measurement, Peltierand thermocouples) and the stimuli are accommodated in the facility infrastructureand are thus independent of the choice of furnace insert.

- Electro-Magnetic Levitation Furnace (MSL-EML)

This is the second facility in the Materials-Science Laboratory and is a follow-ondevelopment of the German Tempus levitation facility. Tempus has been flown on threeSpacelab missions: IML-2, MSL-1, and MSL-1R. The two main objectives of the MSL-EML facility are the following (see Section 2.3.2 also):– Measurement of the thermo-physical properties of industrial alloys, to the high

accuracy needed as input to calculations intended to improve casting processes.On Earth, those measurements are not sufficiently accurate, because most metallicmelts become chemically aggressive at their melt temperature and react withcrucible materials. In microgravity, greatly reduced electromagnetic forces can beused for levitation control in containerless conditions, allowing a large extension ofthe temperature range of the measurements and a reduction in impurity effects.

– Generation of new metallic glasses by strong under-cooling below the meltingtemperature, without the immediate start of solidification. Since there is no contactbetween the melt and container walls, heterogeneous nucleation is avoided.Crystallisation is therefore avoided and the solidification is delayed. Amorphousforms of metallic glass are obtained, with novel technical properties.

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involved requested that a new facility, the Protein-Crystallisation Diagnostics Facility,be built for use on the Space Station.

The PCDF is presently under development as part of the EMIR-2 Programme. It willallow observation and study of the actual crystallisation process of proteins over longperiods in orbit, using advanced diagnostic instruments such as video microscopy,dynamic light scattering and Mach-Zehnder interferometry. It is planned toaccommodate the PCDF in the European Drawer Rack on Columbus.

Since biological macromolecules, including proteins, nucleic acids, viruses, etc., are ofthe utmost importance for living systems, progress in this field is of the highestinterest for basic research and for the pharmaceutical, medical and nutritionindustries. Space research in this field has the potential to yield scientificbreakthroughs if, for example, proteins can be crystallised under microgravityconditions that do not crystallise on Earth.

5.2.3 ESA Facilities and Equipment in the US Laboratory

The co-operative design, development, operation, utilisation and management of theISS is based on an Intergovernmental Agreement (IGA) between the five ISS Partners –the USA, Russia, Japan, Canada and Europe (11 ESA Member States) – concluded inJanuary 1998, and on a NASA-ESA Memorandum of Understanding (MOU). These top-level legal agreements define the objectives and technical capabilities, and also therules of operation and utilisation of the ISS. These rules spell out that the utilisationrights of ISS Partners start with the launch of their hardware contributions. Since theEuropean decision to participate in this programme was taken very late, the launch ofthe Columbus Laboratory was put at the end of the ISS assembly sequence. Thismeans that European utilisation rights start only in late 2004, after the launch of theColumbus Laboratory.

In order to compensate, to a certain extent, for this disadvantage for the European spaceuser community, ESA has concluded a bi-lateral ‘no-exchange of funds’ agreement withNASA. This permits ESA to participate with some experimental equipment andexperiments in the so-called ‘Early Utilisation’ (i.e. in the limited utilisation during the ISSbuild-up phase) in the US Laboratory and in the use of the Station’s external platforms.This bi-lateral agreement is partly based upon scientific co-operation in ESA experimentalhardware, for joint ESA/NASA use in the US Laboratory, as discussed below. It is alsobased upon the delivery by ESA of Laboratory Support Equipment, i.e. the MicrogravityScience Glovebox (MSG), the MELFI –80ºC freezer, and the Hexapod pointing platform forexternal experiments (Fig. 5.2.7), to NASA. In exchange, ESA has also been grantedexperiment accommodation on the ISS’s external Truss structure, as discussed in Section5.2.4. The LSE barter agreement was later extended to give ESA 8.3% of the MSG andMELFI utilisation rights in return for the extension of MSG’s technical capabilities.


in orbit. The intention is to provide a facility that allows quick-turnaround experimentsto be performed within a standardised accommodation package. One of the items tobe located in the EDR is a facility designed for the study of the growth of proteincrystals:

- Protein-Crystallisation Diagnostics Facility (PCDF)

Since the first successful European attempts to crystallise biological macromolecules(of which proteins are one type) on sounding rockets, and later in 1983 on the Spacelab-1 mission, some 400 protein crystal-growth experiments have been performed under microgravityconditions by European scientists, andsome 4000 by US scientists. Proteincrystals of high structural perfection areneeded in order that X-ray diffractionmay be used successfully to reveal thestructures of these macromolecules.Once the detailed structure is unravelled,it then becomes possible to understandtheir function. On Earth, proteins ofteneither do not crystallise or, if they do,they fail to achieve sufficient structuralperfection to allow successful X-raydiffraction analysis.

European protein-crystallisation experiments in microgravity conditions have mostlybeen performed with the ESA Advanced Protein-Crystallisation Facility (APCF). This wasa very reliable facility, but it only allowed ‘blind’ experiments, in which the initialconditions and the final results (when returned to Earth) are known. Only about 25%of the space experiments yielded larger and more perfect crystals than those grownon Earth. Interestingly, some displayed a different morphology to those grown under1g conditions. Why only a fraction of the space-grown crystals were better and indeedresulted in improved structural analysis is not known. Hence, the science community

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Figure 5.2.6. The ESA Protein-Crystallisation Diagnostics Facility,designed for the detailed study of

macromolecule crystallisation and toprovide high-quality crystals for

subsequent X-ray analysis (courtesyof Astrium/DASA)

and angular position/velocity measure-ments and training are supported for thefollowing joint movements: flexure/extension of the knee, ankle, trunk, hip,shoulder, elbow and wrist. It alsosupports force and linear-position/velocity measurements andtraining for multi-joint linearmovements, including whole-arm andwhole-leg linear presses. MARES is ableto support exercise motions/profiles inthe isometric, isokinetic (concentric andeccentric) and isotonic (also concentricand eccentric) modes. It is a large aisle-mounted facility, which has a mass ofsome 200 kg.

NASA is very interested in MARES’scapabilities and has offered to fly it aspart of the NASA Human Research Facility, located initially within the US LaboratoryModule. Launch is planned for June 2002, in conjunction with the Multi-PurposeLogistics Module.

Percutaneous Electrical Muscle Stimulator (PEMS)PEMS is a muscle-stimulator device that was originally developed by ESA for the LMSSpacelab mission, where it was used in combination with the Torque-VelocityDynamometer, the predecessor of the MARES facility. For the ISS, an improved versioncalled PEMS II, with a mass of about 10 kg, is presently under development. It will alsoform part of the NASA Human Research Facility.

PEMS II will support human neuro-muscular research in space by eliciting musclecontraction, using electrodes on the skin. It will permit direct activation of the skeletalmuscles, bypassing the central nervous system’s control. Applying this PEMS mode ofstimuli, it is possible to study changes in muscle function independently of neural-control changes. By applying repeated contractions with PEMS, in combination witha dynamometer like MARES, force-frequency curves, fatigue ability, and the force-length and force-velocity characteristics of muscle capacity can be obtained. PEMSallows the stimulation of single muscles (e.g. the adductor pollicis) as well as entiremuscle groups (e.g. the triceps surae), in combination with MARES.

As a stand-alone instrument, PEMS enables countermeasure protocols of preciseintensity, frequency and duration to be applied, with the objective of preventingmuscle atrophy under microgravity conditions. By evaluating muscle functions, PEMS


- ESA Life-Sciences Equipment

The equipment that has been developedfor joint use by ESA and NASA includesthe following:

Muscle-Atrophy Research and Exercise System (MARES)The MARES facility is a follow-on development of the Spacelab Torque-VelocityDynamometer (TVD) facility flown on the LMS Spacelab mission in 1996. For theInternational Space Station, ESA is seeking to develop a new muscle-researchinstrument that should allow the investigation of atrophy in isolated muscle groups inthe trunk, in joints at the limb extremities, and in complete limbs.

MARES will be used to carry out research on muscle-skeletal, biomechanical,neuromuscular and neurological physiology, to study the effect of microgravity on thehuman being, and to evaluate the effect of countermeasures to microgravity-induced physiological effects. MARES can therefore be used to evaluate the efficiencyof exercise protocols. It enables measurement of the strength of isolated musclegroups around joints or complete limbs by controlling and measuring the inter-relationship between position/velocity and torque/force as a function of time. Torque

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Figure 5.2.7. ESA Laboratory SupportEquipment: the Glove Box, – 80°C Freezer,and Hexapod instrument-pointingplatform

Figure 5.2.8. The Muscle-Atrophy Researchand Exercise System (MARES)

Both facilities use standard experiment containers installed on two centrifuges of 0.6 m diameter. These provide controlled accelerations that range between 10-3 g and2g, for g-response threshold measurements. However, the EMCS experimentcontainers are considerably taller (160 mm) than those of Biolab (60 mm), allowingresearch on larger specimens of fungi, mosses and vascular plants. Plannedexperiments with this cultivation system on the ISS include multi-generation seed-to-seed studies, studies on the influence of gravity on plant development and growth,and g-threshold measurements, as well as experiments on perception and signaltransduction in plant tropism.

There are two moveable zoom video cameras on each of the two EMCS centrifuges,which can be used both for high-resolution observation and down-linking of thepictures for remote analysis.

Within the US Laboratory, the EMCS will occupy the space of four adjacent lockers inthe NASA Express Rack. The long-term continuous operations that will be possible willgive a new dimension to this type of experimentation and considerably broaden plantresearch under microgravity conditions.

Biotechnology Mammalian Tissue Culture FacilityThis facility, designed for cell and tissue-culturing research, will be developed by ESAas part of its future life- and physical-sciences programme. The primary scientificinterest is in studying the influence of the cell micro-environment on cell growth anddifferentiation. The core of the system will allow concentration gradients andmechanical forces to be controlled using fluid-distribution tools, micro-sensors andmicro-actuators. The emphasis will be on mimicking organo-typical conditions and onthe acquisition of data to be used for guided tissue development and differentiationunder both space and terrestrial conditions. In addition to this core cultivation sub-unit, a diagnostic system allows the use of dedicated tools adapted to the particulartissue undergoing testing.

The facility is a modular system, composed of three main components: – An Experiment Sub-unit, which is the core of the system, where the cultivation is

performed under controlled conditions. This sub-unit can be adapted to suit thespecific tissue to be cultivated.

– A Diagnostic Sub-unit, which is a powerful tool for characterising the physiologicaland biological status of the cultivated tissue. This is likely to include a fluorescentmicroscope, combined with laser scanning. For the evaluation of trabecular-bone-tissue evolution, the µCT developed within the on-going Osteoporosis MAP is alsoa likely candidate.

– The Biotechnology Mammalian Tissue Culture Bench, which provides the interfacewith the Experiment and Diagnostic Sub-units, assuming that the facility is to beaccommodated in the European Drawer Rack.


will also be used to judge the efficiency of such countermeasures against thedeconditioning induced by the microgravity environment.

PEMS produces square waves of constant-current stimuli, with a negative post-stimulus lag to ensure charge neutrality. It is programmable to produce sequences ofpulse trains spaced by selectable intervals. The number of pulses in a given pulse train,their duration, amplitude and repetition rate are freely selectable. This complete pre-defined sequence of pulse trains, selected by the medical experts monitoring thehealth of astronauts in orbit, is called the ‘PEMS protocol’.

Hand-Grip Dynamometer and Pinch-Force Dynamometer (HGD-PFD)This device was originally developed by ESA for the LMS Spacelab mission. A rebuiltinstrument was handed over by ESA to NASA in February 2000 for use in the SpaceStation as the first ESA contribution to the Human Research Facility. It will help inevaluating the muscle atrophy in the hands and fingers caused by weightlessness. Itwill also be used for isometric exercising of the hand muscles and as a stressor for theastronaut’s cardiovascular system. Launch of the HGD-PFD is currently planned forApril 2001, but it might be used earlier as part of the ISS Crew Health-Care System. Inparticular, it could be used to evaluate the hand strength of astronauts involved inExtra-Vehicular Activities (EVAs).

European Modular Cultivation System (EMCS)The EMCS and Biolab are complementary ESA biological research facilities. The EMCSwill be launched in 2003 in the US Laboratory, where it will operate for a minimum oftwo years. Biolab, on the other hand, will be launched as part of the initial outfittingof the Columbus Laboratory in late 2004.Both facilities support research thatcontinues and extends the biologicalexperiments performed using Biorack on six Spacelab/Spacehab missions,including research on protoplasts, fungi,callus cultures, algae and seedlings.

In order to provide a better-definedenvironment for plants, both facilitiesare equipped with a dedicated life-support system. This provides a closed atmospheric environment, withconcentration and pressure control forO2, CO2 and N2 and with ethylene-pollutant removal. Humidity, temperatureand illumination are also activelycontrolled.

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Figure 5.2.9. The European ModularCultivation System (courtesy of Astrium/DASA)

in the US Laboratory. The PFM will initially be a core element of the US Laboratory,supporting a wide range of respiratory and cardiovascular measurements.

This co-operation is a first important step towards the principle that all researchfacilities on-board the ISS should be available for use by all ISS Partner scientists,regardless of which agency developed the facility. The wide application of thisprinciple would avoid the duplication of hardware development and lead to a cross-fertilisation of the Partners’ research programmes.

Another step towards optimisation of the research output from the ISS is the agreedco-location of all ESA and NASA human-research equipment, i.e. the ESA EPM and theNASA HRF, in the same ISS laboratory. These plans foresee the concentration of theNASA and ESA life-sciences facilities within the Columbus Laboratory, which willsimplify matters when experiments require the use of scientific instruments belongingto both ISS Partners.

A similar arrangement should be concluded for other disciplines. For example, allgravity-disturbance-sensitive experiments, such as fluid- and materials-scienceinvestigations, should really be performed in the US Laboratory which, because it islocated at the centre of gravity of the overall ISS, has the best steady-statemicrogravity levels.


The development of this facility will build upon the technologies that have beendeveloped for the Gradient Bioreactor, the Advanced Sensor technologies, and theLaminar Flow Bench technology.

Pulmonary-Function System (PFS)As part of the MFC Programme, two other life-sciences modules have also beendeveloped by ESA for early accommodation on the US Laboratory. Forming part of theNASA/ESA Pulmonary-Function System, they are:– the ESA Photo-Acoustic Analyser Module (PAM) – the ESA Pulmonary-Function Module (PFM).

The PFS is a ESA/NASA collaborative development in the field of respiratoryphysiology and cardiovascular instrumentation, which will be integrated into the USLaboratory. NASA’s contributions to the joint PFS are:– the NASA Gas-Analysis System for Metabolic-Analysis Physiology (GASMAP)– the NASA Gas-Delivery System (GDS).

Through in-orbit reconfiguration of the interconnections between the four units, it willbe possible to create two different respiratory instruments. The first, called MAS (Mass-spectrometer-based Analyser System), uses the building blocks of GASMAP, PFM andGDS. The second, called PAS, involves the use of PAM, PFM and GDS.

The PAS configuration will be portable, permitting it to be used not only in the USLaboratory, but also in other ISS modules, such as the Russian Zvezda habitationmodule.

GASMAP will be used to measure and analyse the inhaled and exhaled breath ofhuman subjects. At its core is a random-access mass-spectrometer, which allows theconcentrations of the various gases in the mixtures being breathed to be analysed.

GDS provides the special gas mixtures needed to calibrate GASMAP and PAM. Itconsists of a part that remains permanently in orbit, and a re-supply part consistingof a high-pressure cylindrical reservoir, a pressure regulator, a stop valve and amechanical pressure gauge.

PAM is a further developed and miniaturised version of the Respiratory MonitoringSystem-2 flown on the Euromir ’95 mission. It will provide the means to determine theconcentrations of O2, CO2, CO, SF6, methane and freon in the respired gas mixture. Thismixture may also contain significant amounts of N2 and water vapour.

The PFM consists of the Respiratory Valve Unit (RVU), flow meters, a re-breathing bagand an electronics unit, all accommodated in a transportable standard drawer toenable the PAM to be used outside the NASA Human Research Facility accommodated

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Figure 5.2.10. The ESA Photo-AcousticAnalyser Module, designed to analysehuman respiratory gases. It provides anon-invasive method of determiningcardiac output, lung volume and lungfunction

5.2.4 ESA Microgravity Experiment Equipment for ISS External Platforms

As a result of the bilateral agreement with NASA, some ESA-providedviewing/exposure experiments can be accommodated on three ‘Express PalletAdaptors’ at NASA’s external viewing sites. These are located on the Station’s trussstructure and can be used during the early-utilisation phase.

Since there is a large demand in Europe for external experiment accommodation onthe Space Station, as shown by the replies to the 1997 Announcement of Opportunity,ESA decided to add to the Columbus Laboratory four standard Express Pallet Adaptors.Each of these has a 1 m2 mounting surface and a mass-carrying capability of 225 kg.


- Physical-Sciences Equipment

The first element of the ESA Materials-Science Laboratory (MSL-1), will be temporarilylocated in the US Laboratory. Its characteristics have been discussed in detail inSection 5.2.2, together with the arrangements made with NASA for it to beaccommodated for the first two years (from 2003) in the US Laboratory.

Table 5.2.2 summarises the planned major NASA research facilities to beaccommodated in the US Laboratory ‘Destiny’ and in the Centrifuge AccommodationModule (CAM). It also lists the ESA contributions accommodated in ‘Destiny’ and theCAM.

Table 5.2.3 lists the planned Japanese research facilities to be accommodated in thepressurised Japanese Experiment Module (JEM), recently renamed ‘Kibo’.

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Table 5.2.3 Planned Research Facilities for the Japanese ‘Kibo’ module (JEM)

Payload Element Research Area Technical Features

Gradient Heating Facility Directional Solidification Automatic exchange of sample(GHF) Semiconductor Growth from Vapour cartridges (max. 15)

Phase 3 independent heating zones Max. Temperature: 1600°C

Adv. Furnace for Microgr. Semiconductor Crystallisation and Ellipsoidal Mirror Furnace,Expts. with X-ray Study of Marangoni Convection with Observation in real-time,Radiography (AFEX) X-Rays in Gas Atmosphere isothermal and gradient heating

modes, up to 1600°C

Fluid-Physics Experiment Study of Marangoni Convection to 3D flow-field observationFacility (FPEF) remove Air Bubbles in Floating-Zone surface – flow rate

Semiconductor Crystal Growth determination

Solution-Growth/Protein- Crystal Growth from Solution 2 Sub-Units: SolutionGrowth Facility (SPCF) Growth of Large Protein Crystals for Crystallisation Observation Fac.

Structural Analysis on Earth (SCOF) with Interferometers, andProtein Crystallisation Res. Fac.(PCRF)

Cell Biology Experiment Effects of Space Environment on Cells, Variable g-levels provided byFacility (CBEF) Tissues, Small Animals, Plants and turntable for reference experiments.

Micro-organisms Samples accommodated in canisterson turntable and incubator

Clean Bench (CB) Provides Aseptic Operation for Life CB has disinfection/sterilisationSciences and Biotechnology Expts. chamber using UV-lights and

Cell Experiment Unit (CEU)

Biological Experiment Units Plant Life-Cycle Experiments, Cell BEU exists in 2 versions: (BEU) installed in CBEF Culture Expts. using Phase Contrast and Plant Experiment Unit (PEU) and or CB Fluorescence Microscopes Cell Experiment Unit (CEU)

Minus Eighty Degree Support Life Science and MEFI is developed by ESA andFreezer (MELFI) Biotechnology Experiments with Storage bartered with NASDA for ISS

at +4°C, –26°C and –80°C Payload Racks.

*Kibo means Hope. Kibo is planned for launch with payloads in 2004

Table 5.2.2 Planned Major NASA Research Facilities for the ISS

Payload Element Research Area Launch ESA – Contrib. or Barter Comments

Human Research Biomed Research. Human Physiology 2001 Contrib.: Handgrip DynamometerFacility-1 + Psychology4 Express Racks Multidisciplinary 2001 –

Microgr. Science Glovebox Biotechn., Combustion Mat. Sci. 2002 } Dev. by ESA as barterMinus 80°C Life Sci. Freezer Life Sciences 2002 } for early flight opportunitiesWindows Observational Fac. Earth Observation 2002 –Human Research Facility-2 Biomedical Research 2002 ESA Contrib.: Pulmonary Funct.

Module PAM, MARES, PEMS

Alpha Magnetic Spectrometer Space Physics (Anti-Matter Physics) 2003 International Sci. Cooperation

Habitat Holding Rack-1 Gravitational Biology 2004 Europ. Mod. Cultiv. Syst. (EMCS)Material Science Res. Fac.-1 Materials Sciences 2004 ESA Mat. Sci. Lab.-1Fluids and Combustion Fac-1 Combustion Science 2004 –Life Sciences Glovebox Biomed. Res., Biotechn., Gravit. Biol., 2004 –

Ecology

Biotechnology Res. Fac. Protein Crystalisation, Bioreactors 2004 Accommodation in JEMX-ray Crystalography Fac. Prel. Structure Determin. of Proteins 2004 –Advanced Human Support Testbed for Long-duration Flights 2004 Accommodation in JEMTechnology

Habitat Holding Rack-2 Gravitational Biol. + Ecology 2005 –Fluid and Combust. Fac-2 Fluid Physics 2005 –Stratosph. Aerosol & Gas Exp. Atmospheric Physics, Earth Science 2005 –Express Pallets 1 and 2 Multidisciplinary 2005 Accom. of ESA Ext. Payload

incl. Hexapod PlatformFluids and Combust. Fac-3 Fluid Physics 2005 –Express Rack Multidisciplinary 2005 –Express Pallet 3 Multidisciplinary 2005 Accom. ESA External Payload


However, these ESA external viewing sites will only be available after the launch of theColumbus Laboratory in late 2004.

The Russian ISS modules also offer the possibility to attach external experimentequipment. A contract has therefore recently been concluded with the Russian spaceauthorities to accommodate the ESA radiation biological facility ‘Matroshka’ on theouter surface of the Russian service module ‘Zvezda’ in early 2003.

The ESA external payloads Expose and ACES, which will be mounted on NASA ExpressPallets (a Pallet houses six adaptors, each with about 1 m2 of mounting surface forexperiment accommodation), and the Matroshka facility are described below.

- Exobiology Experiment Unit (Expose)

Expose is to be mounted, together with the European space-science payload Sport, onone Express Pallet Adaptor, oriented towards the Sun. The unit accommodates eight selected exobiology experiments on a coarse-pointing mount that tracks the Sun, thedirection of which changes rapidly as the ISS moves through its orbit with a gravity-gradient orientation.

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ColumbusExternal PayloadFacility (4 ExPAs)

Figure 5.2.11. The locations for attaching external payloads to the ISS

Port UnpressurisedLogistics Carrier

(ULC)/Payload Attach Site (2)

JEM ExposedFacility Sites (10)

Mobile Servicing System

Starboard Payload AttachSites (4) =24 ExPAs

Figure 5.2.12. The core Pharao element of the ACES atomic clock (courtesy of CNES)

The exobiology experiments will expose a large number of biological specimens for upto 1.5 years to free-space conditions and/or selected space parameters such as solarUV radiation, cosmic radiation, space vacuum and temperature extremes. Expose willalso support long-term in-situ studies of microbes in artificial meteorites, as well asthose of microbial communities from special biological niches (see Section 2.2.3). Theexperiments include studies of photo-biological processes, in simulated planetaryradiation environments (Mars, early Earth, ozone layer) as well as studies of theprobabilities and limitations of life in the Solar System.

The results from Expose experiments are expected to provide a better understandingof the processes regulating the interactions of life with its environment on Earth.

- Atomic-Clock Ensemble in Space (ACES)

ACES is a co-operative CNES/ESA project under ESA management, the core element ofwhich is a laser-cooled caesium clock (Pharao). This is a French contribution, designedby the Ecole Normale Superieure, for which Neuchatel Observatory (CH) is providing aspace version of a hydrogen-maser clock (SHM) to act as a reference. Other ACESelements are Time Transfer by Laser Link, for the synchronisation of remote clockswith an accuracy better than 50 picosec, an All-weather Microwave Link, which is tobe used for time and frequency comparison to picosecond accuracy, and a PreciseOrbit-Determination Device to provide altitude and velocity determination for the ISS.Further elements are a Frequency Comparison and Distribution Package, allowingPharao and SHM phase comparison and signal transfer to the time-transfer systems.

ACES exploits the combination of laser cooling (Fig. 5.2.12) and microgravity toproduce slow-moving atoms, which allows 10 times longer interaction times than arepossible on Earth. This, in turn, leads to a narrower resonance frequency width, anincreased signal-to-noise ratio, and thus greatly increased measurement precision. Afactor of 100 improvement, to 10-16/day, is expected. A major goal of the ACES projectis the characterisation of Pharao by comparison with the on-board space hydrogen-maser clock (SHM) and with primary ground clocks via a laser or microwave link.

ACES opens up not only new opportunities in fundamental research, such as themeasurement and testing of relativistic effects, but also important applications inatmospheric propagation, high-precision geodesy, navigation (improved GPS) andadvanced communications. It is planned to install ACES on a nadir-viewing (Earth-looking) ISS Express-Pallet Adapter for a three-year period (Fig. 5.2.14).

- Body Radiation-Dosage Measurement Unit (Matroshka)Matroshka is a tissue-equivalent phantom representing the upper part of the humantorso. It is to be used to study the depth-dose distributions for different componentsof the particle and radiation fields in orbit, looking at the different positions thatcorrespond to the organs of astronauts. The dummy is equipped with user-providedpassive and/or active detectors for ionising radiation.

The body phantom consists of commercial ‘Rando’ phantom parts, familiar in the fieldof radiotherapy, i.e. various types of tissue simulating the human organs in terms ofsize, shape, mass, density, orientation and nuclear interaction. Knowledge of theradiation dosage to which the sensitive organs of astronauts’ bodies are exposed isvery important for evaluating the risks from radiation on the ISS, including extra-vehicular activities, and for future long-duration space missions.

Matroshka will be launched in early 2003 on a Progress spacecraft andaccommodated for one year on the outside of the Russian ISS service module Zvezda.


Figure 5.2.13. The ACES package to be installed on the ISS (courtesy of CNES)

Figure 5.2.14.

Formal Announcements of Opportunity (AOs) will be published regularly, solicitingproposals from the user community for specific research topics. These topics arerepresented at the lower levels of the pyramid in Figure 5.3.1. The typical time scalefor the updating of user inputs is one year, which means that changes in topics ofinterest can be introduced rather rapidly. These topics are then synthesised, under theguidance of the ESA expert advisory groups, into research priorities and top-levelobjectives. These will have a typical variation time scale of 3 – 5 years, i.e. the durationof the programme itself. These top-level objectives are again used as inputs for theAOs, thereby creating a programme-stabilising feedback loop.

The user inputs at the base of the pyramid are used to define the specific activitiesbeing carried out within the programme, including defining the need for flights ofexisting facilities or the development of new ones. It is the intention that each of theseproposals should encompass a complete research programme, including anynecessary ground-based research, rather than just describing an individual flight (ISSIncrement) experiment.

At present, the time required for the development of a new facility is in the order of 3 – 5 years. It is the goal in the ISS era to shorten the time span between thesubmission of a proposal and the execution of an experiment to 1 – 3 years,depending upon the specific hardware requirements. In exceptional cases, such asexperiments with a highly competitive element or with high industrial or commercialinterest, this time should even be reduced further.

5.3.3 The Selection of Research Objectives

The definition of the top-level research objectives is a continuous process, in which allof the parties mentioned above play a role. In particular, several meetings haverecently taken place with the ESA advisory teams, the European Science Foundation(ESF) and the national delegations. The selected future research objectives have been


5.3 A Future European Life- and Physical-Sciences Research Programme

M. Heppener

5.3.1 Introduction

European life- and physical-sciences research in space stands at the threshold of a newera. Over the next few years, there will be a progressive build-up of research activitieson the Space Station, culminating in the introduction of science operations in the ESAColumbus Laboratory. At that point, the facilities will be in place for ESA to mount along-term scientific research programme in space. It will finally become possible forEurope to embark upon a programme that has both depth and extent, and one thatcan be carried out at a rate and with a quality that can stand direct comparison withits terrestrial-based counterparts.

To support such a programme, it will be necessary for ESA to seek approval andfunding from its Member States both for the exploitation of the ISS as a whole, and forthe proposed Life- and Physical-Sciences and Applications Programme. Discussionsand decisions on these topics are due to take place in the course of 2001.

In looking towards that future of an enlarged activity and increased scientific output,ESA is now concerned to ensure that such an activity takes place within a frameworkthat closely co-ordinates both European and national endeavours in this field. Indefining the plans that will lead to the appropriate scientific output, ESA intends tocontinue and to expand its close consultations with an enlarging user community. Itwill also give increasing support to processes that will further facilitate the transfer oflife- and physical-sciences research results into the mainstream of relevant terrestrialresearch programmes, as well as into potential applications and industry. Those linksbetween research and applications that already exist, together with the programmesdesigned to support increased industrial involvement, will be strengthened evenfurther. Last but not least, greater efforts will be made to involve the general public inthese developing activities and to increase public awareness of the benefits to life thatflow from space research. The manner in which these changes will be brought aboutis outlined below.

5.3.2 A User-Driven Programme

The starting point for the future programme is provided by the inputs from the usercommunity. Figure 5.3.1 is a graphical representation of the essential ingredients ofthis user-driven approach.

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Figure 5.3.1. Schematic of the principal ingredients of the future programme

- Innovating Technologies and Processes

With the progress made in life- and physical-sciences research in space during the pasttwo decades, research topics have emerged that have a clear relevance for industrialproduction processes and the development of new technologies. In the life-sciencesarea, this is the field of agriculture and biotechnology, genetic improvement of plantgrowth, analytical bioreactors, gene chips, reconstituted tissues for drug screeningand artificial organs. In the physical sciences, there is a need for understandinggravity-dependent processes in order to be able to model and improve the productionmethods. Examples include improved knowledge of critical parameters for the oil andcasting industries, modelling of combustion and crystallisation processes, and thedevelopment of advanced materials such as metallic foams. Also, techniques that arepresently employed for their basic research potential, such as high-precision cold-atom based systems and advanced plasma-based technologies, will be stimulated tofurther develop them into practical applications.

- Energy and Environment

Several of the topics addressed in projects that are currently running have relevancefor understanding, or even improving, processes that have an environmental impact,address safety issues, or deal with energy-production techniques. Examples includethe studies of atmospheric dust and geophysical flows, both of which have a clearimpact on the modelling of the Earth’s climate. The safety of the nutrition cycle is alsoa very relevant present-day application, which is being studied within the frameworkof developing closed-loop life-support systems. Finally, a lot of attention is devoted insome selected proposals to a better understanding of combustion and heat-transferprocesses. Here, researchers and industries hope that a better understanding of thebasic chemical and physical aspects of combustion will lead to higher efficiencyenergy-production techniques and/or cleaner engines.

5.3.4 The Alignment of Strategic Objectives with Other European Institutions

An important aspect of the future programme will be its integration within a largerEuropean scheme. In particular, it is the intention to identify common objectives withthe most important institutions dealing with research in Europe. By using commonobjectives, and even common terminology, it should be possible to achieve:– a continuous dialogue with the major European players on strategic and

implementation issues– increased embedding of space-based research into ground-based research

programmes– easier access to other funding sources for scientists active in space-based research– increased appreciation and underpinning at the level of science policy makers.


presented to the scientific community at large at an ESF-organised workshop and,following a critical appraisal, the list will now be finalised. Presently, four top-levelobjectives have been identified, which are briefly described below.

- Exploring Nature

In any scientific discipline, unbiased curiosity is the starting point for progress.Generally, the results of basic research will lead to new ideas both in the area of thepure sciences and in the process of finding new applications. The research prioritiesthat have been established in this area follow from recently received proposals, as wellas common trends in the respective disciplines. In the life sciences, the emphasis is onunderstanding gravity’s influence on basic biological processes, such as cell growthand differentiation, gravitaxis, developmental biology and tissue organisation. In thephysical sciences, topics include the study of solidification processes, the organisationof matter (supercritical fluids, strongly coupled plasmas, cosmic and atmosphericdust, diffusive mechanisms) and non-classical physics, such as quantum liquids andtheir application in atomic clocks and relativity tests.

Special attention will be given to the human exploration of the Solar System, whichwill be one of mankind’s great endeavours in the 21st century. Motivations for this willbe the search for extraterrestrial life and the desire to explore the unknown. Inresponse to recent AOs, proposals have been received that address this domain, suchas exobiology studies and the development of life-support systems. In addition,specific topics will be promoted for future study, including areas such as human-physiology and psychological aspects, radiation studies and the development of in-situ production technologies.

- Improving Health

A major part of the proposals, and of the human-physiology experiments supportedby the Agency today, deal with health-related topics. In particular, the spaceenvironment provides a good tool with which to study the effects of disease andageing and the underlying mechanisms, to identify suitable clinical treatmentmethods, and to develop advanced diagnostic equipment. Several projects alreadyapproved by ESA address the study of physiological adaptations as a result of reducedloads and immobility, such as blood-pressure control, muscle atrophy, balancecontrol, osteoporosis and cognition. Also, specific attention will be given to theinfluence of environmental conditions, atmosphere, nutrition, and radiation on healthand safety. Several diagnostic tools are presently under development, building uponnon-invasive techniques, miniaturisation, advanced sensors and tele-monitoring,which will be employed during future spaceflight missions. Clinical countermeasuresfor rehabilitation, including exercise devices, drug tests and special food will also betested.

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projects in human physiology and medical applications carried out in the ESAprogramme, such as osteoporosis studies and countermeasures. Other examples arethe ESA projects in applied material, fluid and combustion sciences, which may leadto important competitive advantages for European industry.

5.3.5 Consolidation of a European Strategy with the National Authorities

Given the budgetary pressures in Europe in the area of space activities, it is essentialthat the contents of the future ESA programme be agreed upon by the national spaceauthorities. Duplication of activities should not only be avoided on a case-by-casebasis, but its avoidance should also be a key driver in designing both the ESA and thenational programme activities. Already today, the need for a unified Europeanapproach is evident from the increasing number of bilateral agreements betweenNASA and individual Participating States. This trend ultimately weakens European-wide space efforts and runs counter to the political processes represented by theEuropean Union. It will clearly also lead to sub-optimal use of European resources andis not in the long-term interests of the European taxpayer.

Therefore, the goal is that ESA’s research activities and those carried out by thenational space agencies must find their place within the framework of a EuropeanResearch Strategy. The partners in this overall strategy will still be able to recognisetheir own contributions and priorities. However, they will now be part of an integratedapproach. This not only creates greater clarity towards the funding authorities, but isalso of advantage in, for example, discussions with the Space Station partners. Finally,the implementation of this European Research Strategy will also lead to an overallEuropean approach towards the definition and development of future payloads andfacilities, based on user inputs.

5.3.6 The Role of European Industry

Traditionally, European industry was active in the fields of life and physical sciences asdevelopers of advanced facilities and instrumentation. This has led to a veryimpressive technological knowledge base, with European space-research facilitiesamong the most sophisticated presently available. Within the framework of a user-driven programme, this will be a very important asset, since here the developingindustries will have to have a thorough understanding of the scientific requirementsand translate them into engineering specifications. A specific challenge will be toreduce the time from initial conception to flight of an experiment to something in theorder of two years, and to do so with significantly lower budgets than were availablein the past.

The reason for this is that only by applying these two conditions can the ISS becomethe high-throughput laboratory that everybody wants it to be. In view of the relatively


The various National Research Councils decide the policy for basic scientific researchat the national level. Almost all of the national organisations responsible forsupporting scientific research are associated with the European Science Foundation,which has as its prime objectives to:(a) advance co-operation in basic research(b) examine research issues of strategic importance(c) give advice on science policy matters(d) promote the mobility of researchers and the free flow of information and ideas(e) facilitate co-operation in the use of existing facilities and in the planning and

provision of new facilities(f) plan and, where appropriate, manage collaborative research activities.

The ESF is therefore judged to be a valuable counterpart for strategic discussions onbasic research objectives. Contacts were established in 2000 and agreement hasalready been reached that the ESF will participate in this process and also organiserelevant workshops to review the proposed objectives.

In the area of applied research, the European Commission (EC) is the obviouscounterpart for ESA. The Framework Programmes (FPs) define the EC’s strategicpriorities for research, technological development and demonstration activities. Thepresent Framework Programme No.5 covers the period 1998 – 2002, and thedefinition of the next programme (FP6) is underway.

The current programme (FP5) has been conceived in order to help solve problems andto respond to major socio-economic challenges such as increasing Europe’s industrialcompetitiveness, job creation and improving the quality of life for European citizens.Emphasis is placed throughout on the process of innovation, so as to ensure that theoutput of EU research is translated into tangible results. A total budget of 14.96 billionEuros has been allocated to implementing FP5, which comprises four ‘ThematicProgrammes’ and three ‘Horizontal Programmes’:– Quality of Life and Management of Living Resources– Promoting a User-Friendly Information Society– Competitive and Sustainable Growth– Energy, Environment and Sustainable Development– Confirming the International Role of Community Research– Promotion of Innovation and Encouragement of Small- and Medium-size-

Enterprise Participation– Improving Human Research Potential and the Socio-Economic Knowledge Base.

There are obvious overlaps at several points with the objectives of the future ESAprogramme in life- and physical-sciences research in space. For example, one of thekey actions of the Quality of Life theme is called ‘The Ageing Population andDisabilities’. Research projects receiving funding here have the same themes as

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small scale of individual facilities, this work is of particular interest for spacecompanies in the smaller ESA Member States, or for Small and Medium-sizedEnterprises (SMEs). This makes the programme of life- and physical-sciencesresearch in space also very attractive in the context of European industrialpolicy.

A new class of industries previously not involved in space research are non-space companies that are interested in using space as a tool. Within theframework of recent AOs, more than 48 Microgravity Application Project(MAP) proposals with a high application value and with industrial researchersas part of the teams have been accepted. In total, more than 125 companiesare involved in these projects, including several major internationalcompanies and a number of small, high-technology companies aiming forspecific markets. This very promising development is regarded as the first signof truly industrial research being conducted in space.

5.3.7 Explaining to the General Public

The objectives of the future programme have been established by analysingthe requirements of the four categories of parties that are directly involved, i.e.the active users who have submitted proposals, the European researchcommunity at large, the various national space agencies, and Europeanindustry. It should not be forgotten however, that in the end the support forthis activity depends upon the ability to explain its usefulness to the generalpublic. Since the sixties, there has been a continuing interest from the generalpublic in space activities, which actually seems to be growing stronger inrecent years. However, for the moment astronomical topics and flights byastronauts attract the greatest attention. As has been amply demonstratedabove, both in the life and physical sciences excellent examples exist ofresearch results that are of direct relevance for health problems, to the welfareof the environment, or for the development of new materials and processes.

It is the future responsibility not only of ESA, but of all those involved, to makethe results of these efforts known, to explain and demonstrate that the life-and physical-sciences research that is carried out in space is not some esotericexercise, but is for the ultimate benefit of life on Earth.

CHAPTER 6. APPENDIX6.1 Programmatic Structure of ESA's Microgravity Activities

G. Seibert

Research in materials science/fluid physics and life sciences is a basic scientificactivity, although the results are often later applied in industrial processes or inmedical treatments on Earth. At the time of each decision on ESA’s MicrogravityProgramme phases, therefore, the question of whether the programme should beadded to the mandatory traditional Science Programme (astrophysics, astronomy,atmospheric physics), or whether it should be an optional programme in its own right,has been discussed.

In ESA terms, ‘mandatory’ means that every Member States must participate in theprogramme with a contribution proportional to its Gross National Product (GNP). Thecurrent ESA Mandatory Programme includes the Science Programme and the GeneralBudget, which covers the Technology Research Programme (TRP) and a number ofadministrative activities needed for the functioning of the Agency. The other ESAprogrammes, such as Launchers (Ariane), Earth Observation, Communication/Navigation and Manned Spaceflight and Microgravity, are so-called ‘OptionalProgrammes’. These allow ‘à la carte’ participation, with each Member State free todetermine the size of its contribution (as a percentage or an absolute amount) to theprogramme’s financial envelope, with no obligation to participate in a follow-onprogramme or even a small extension of the programme envelope. An OptionalProgramme can also find itself with a cumulated Member State subscription of lessthan 100% of the ESA-proposed budget envelope. Such a situation is only acceptableif a proposed programme consists of a number of independent elements, where thedeletion of one element, in order to match the available level of subscription, does notaffect the others.

Although the adoption of a mandatory status for ESA’s Microgravity Programme wasrequested by several smaller Member States at each programmatic decision point, thisstatus was never achievable. The reasons for this were the following:

– Not all ESA Member States wanted to participate in this programme, e.g. Ireland,Finland, Norway (except for EMIR-1).


– At the ESA Ministerial Conference in September 1995, two different and independentMicrogravity Programme phases were approved, which started in 1997: (i) Theutilisation programme EMIR-2, as the follow-on to EMIR-1, providing researchopportunities in the pre-Columbus era, and (ii) The Microgravity Facilities forColumbus (MFC) programme, in which ESA’s major microgravity multi-user facilitiesfor the ISS utilisation phase (presently planned to start in early 2005) are beingdeveloped.

– The EMIR-2 programme phase was extended in 1999 (EMIR-2 Extension) by a smallamount (about 50 MEuros) to compensate somewhat for the original low financialenvelope and to cover some flight opportunities in the pre-Columbus era, which wasstill further extended to 2003 and 2004.

– The Columbus programme content includes a ‘Utilisation Promotion’ element,which was foreseen to promote ISS utilisation by all user disciplines, such as spacescience, Earth observation, technology and microgravity research and some userinformation activities. The microgravity share of this promotion budget is used tosupport microgravity application projects in which industry is actively participatingin the applied research.

6.2 ESA Facilities on Spacelab and Spacehab

The most important research opportunities supported by the ESA Phase-1, EMIR-1 andEMIR-2 programmes in the 1980s and 1990s were the eight Spacelab missions andlater the Spacehab missions.

A short description of Spacelab and the commercially offered Spacehab is provided inSection 1.2. For 15 years, from 1983–1998, the manned laboratory Spacelab was theworkhorse of microgravity research for the ‘western’ world. It provided adequatetechnical resources, acceptable microgravity levels (10–4 g) for the great majority ofmicrogravity experiments, and up to seven astronauts for the operation and repair (ifneeded) of the experiments. The crew were also available as subjects for humanphysiological studies. Several of the astronauts on each Spacelab flight, the so-called‘Payload Specialists’, were competent and trained in the subjects of theexperimentation.

The 7 to 17-day duration of Shuttle/Spacehab missions was also adequate for the firstgeneration of space experiments, which did not yet require a series of experimentalruns with parameter variations, as normally applied in the terrestrial laboratory.However, the Shuttle/Spacelab flight frequency was too low, at least for the Europeanscientists who had, at best, one flight opportunity for their experiments every twoyears.


– A few of the larger Member States (like the UK) did not want to contribute to a levelcorresponding to their GNP.

– Besides their participation in the ESA Microgravity Programme, the two largestcontributors to other ESA programmes, Germany and France, had their ownnational microgravity research programmes. During the 1980s and early 1990s, theGerman national programme was actually larger than the ESA programme.

– Europe did not possess and was not developing its own man-rated launcher system,nor had it mastered the re-entry techniques needed for retrievable satellites. Thismade the major elements of ESA’s Microgravity Programme dependent upon US orSoviet launch and retrieval systems, a fact that made the long-term planning andfinancing of microgravity research opportunities uncertain.

The consequence of this situation at European level was that a large number ofpartially overlapping phases of the ESA Microgravity Programme, with only limiteddurations and different Member-State percentage contribution levels, were approved.

Figure 6.1.1 shows that seven, programmatically different, microgravity activityphases were approved and executed, some of which are still on-going until 2004. Italso shows that:

– In parallel with the Phase-1 of the Microgravity Programme, the Eureca Programme,which included a microgravity core payload, was approved in 1983. Due to thedelays caused by the Challenger accident, the development of this core payloadwas stretched over many years and Eureca was eventually flown only once, in1992/93.

– The EMIR-1 programme is by far the largest ESA Microgravity Programme phase.

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Figure 6.1.1. Development of ESA’s budget for microgravity research and facilities

Mill

ion

Euro

s


Table 6.1. Multi-User Facilities on Spacelab Missions Used to Perform ESA-Selected Experiments

Mission SL-1/FSLP D-1 IML-1 D-2 IML-2 USML-2 LMS Neurolab

Launch 28-11-83 30-10-85 22-01-92 26-04-93 08-07-94 20-11-95 20-06-96 17-04-98

Mission 10 days 7 days 8 days 10 days 15 days 16 days 17 days 16 days

ESA Share 50% 38% 25% 25% 35% 10% 35% 25%of Payload

Mat. Science Biorack Biorack Anthrorack Biorack Glove Box Torque Velocity Visual andDouble Rack, Dynamometer Vestibularincluding: Space Sled Biostack Biostack Biostack Investigation• Isothermal Percutaneous System (VVIS)

Heating Fluid- Critical Lymphocyte NIZEMI (D) APCF Electrical with HumanFacil. (D) Physics Point Instrument (2 flight Muscle Off-axis

• Gradient Module Facility units) Stimulator RotatorHeating (FPM) (CPF) Advanced Advanced (PEMS)Facil. (F) Fluid- Protein

• Mirror + several Physics Crystallisation Advanced + severalHeating German Module Facility Gradient European PIFacility (D). facilities (APCF) Heating Instruments

Microgravity (2 flight units) FacilityFluid Physics Measurement (AGHF)Module (I) Facility Bubble Drop BDPU+ other PI (MMA) and instruments Particle Unit APCFin MS/FS. (BDPU) (2 flight units)

3D- MMABallistograph (I)Biostack (D)

Echocardio-graph (F)

Lymphocyte Proliferation Instrum. (CH) Biorack

Total No. 70 82 36 88 79 30 43 26of Expts.

Phys.Science 36 54 8 38 24 24 -Experiments

Life Science 16 26 28 41 53 LS+ 16 26Experiments PS only

Others 18 2 - 9 2 3 -

(D), (F), (I), (CH) mean that the payload element was provided by these ESA Member States.

Facility/Missions Field of Research Size of Facility Special Technical Features

Cell and developmental biologyon bacteria, unicellularorganisms, human cells, plantgravi-perception and gravi-tropism. Embryogenesis,organogenesis

Vestibular receptor system,visual system, somato-sensorysystems, i.e. mechano-receptorsin skin, joints and other tissue

Study of static and dynamicliquid columns of differentviscosity, characterisation ofMarangoni convection, studyof capillary forces

Capillarity, wetting, liquidfloating-zone stability,Marangoni convection

Phase transitions, phaseseparation and compressibilitynear the critical point of SF6.Interfacial phenomena inmicrogravity

Cardiovascular, cardio-pulmonary and endocrinologyresearch in humans

Study of particle, drop andbubble dynamics and growth intransparent liquids. Steady andoscillatory Marangoni-Bénardconvection, thermo-capillaryinstability, nucleation/condensation

1. Biorack:(6 missions)

SL : D1, IML-1 & IML-2Spacehab: MM3, MM5and MM6

2. Vestibular Sled:SL-D1

3. Improved Fluid-Physics Module:SL-D1

4. Advanced Fluid-Physics Module:SL-D2

5. Critical-Point Facility:SL: IML-1SL: IML-2

6. Anthrorack:SL-D2. Parts of it onNeurolab SpacelabMission

7. Bubble Drop andParticle Unit:SL: IML-1SL: LMS

1.5 Standard Racks

350 kg

3.5 m long Sled structureon SL centre aisle, plus 2SL single racks for controland storage.

550 kg

80 kg, accom. inMaterials-Science DoubleRack

96 kg

1/2 of an SL StandardRack

1/3 of an SLStandard Rack

90 kg

2 SL Standard Racks

610 kg

1 SL Standard Rack

270 kg

Incubators (2), glove box,cooler/freezer, 1g centrifuge,standard experiment containers,late-access Mid-Deck Lockers

Performs pre-programmed velocitytrajectories with sinusoidal andtriangular waveforms plusoscillating motion.Vestibular helmet with opticalstimulation and IR-TV recording

Rotates axisymetrically and non-axisymetrically different shapesof liquid bridges. Applies lateralmovements, vibrations, electricalfields and has heating capabilities

Visualisation of shape and fluidmotion. Surface temperaturesmeasured with thermographiccameras

Very accurate temperature controlof 0.1mK, in temp. range 30-70°C.Optical diagnostic, withinterferometry and light scatteringwhen passing through the gas-liquid critical point

Used often in combination with theLower-Body Negative PressureDevice and Ergometer.AR elements: breath analyser withmass-spectrometer, echo-cardiograph, ECG, EOG, EEG, high-speed blood centrifuge, gas supplyfor pulmonary research

Injection of bubbles and drops influid cells. Optical diagnostics.Application of temperaturegradients and electric fields.Sophisticated individualexperiment containers

Table 6.2 ESA Microgravity Multi-User Facilities for Spacelab/Spacehab

6.3 ESA Experiments and Facilities on Bion/Foton

In 1987, ESA started a co-operation with the Soviet Institute for Biomedical Problems(Moscow) to fly biological experiments on the Soviet retrievable satellite Bion (alsocalled Biocosmos or Biosputnik), which had been flown since 1973. Technicallyspeaking, Bion was the same as the ‘Foton’ spacecraft, which is now offeredcommercially as a retrievable satellite. The ground landing of these spacecraft issmoothed by a retro-rocket system. The spacecraft itself consists of three sections: adescent module, a battery package as the main energy source for spacecraft andpayload, and an attitude and orbit control module, with gas thrusters and a rocketengine used for re-entry. The payload-carrying capability of Bion/Foton is about 500 kg, with an average power provision of 400 W (peak 700 W) for a typical missionduration of two weeks.

Three autonomous experiments were provided by selected ESA and Soviet PrincipalInvestigators for the Bion-8 flight in 1987. ESA then participated in the Bion-9 missionin 1989 with five joint experiments. For the co-operation on Bion-10 in 1992, ESAdeveloped the Biobox multi-user facility to support cell and developmental biologyexperiments. During its first flight on Bion-10, the Biobox was used by fourexperiments, and in addition six autonomous joint ESA/Soviet experiments wereperformed on this mission.

To ease the effects of the gap in Shuttle/Spacelab flight opportunities, from 1990onwards ESA increased its use of these Soviet retrievable satellites, also on a


Facility/Missions Field of Research Size of Facility Special Technical Features

Alloy-solidification studies,semiconductor crystal growth. Planar-front solidification,cellular and dendritic growth.Miscibility-gap studies, phase-separation studies, compositematerials

Muscle-disuse atrophy studies.Efficiency of countermeasures(isokinetic exercise better thanisotonic ergometry training).Muscle force, velocity ofmovements and endurancetests

Human neuro-physiologicalresearch. Sensation ofcentrifugal forces without Earthgravity. How sense of spaceorientation is organised in thebrain

Growth of large protein singlecrystals, for 3D structuredetermination of protein macro-molecule with X-ray diffractionanalysis

A facility for preparation,handling, and performance ofsimple experiments in physical-and life-sciences fields.Handling of toxic materials

In-situ observation of directionalsolidification in organic alloysused to model metallic melts

Measurement of the dynamicresponse of surface tension to amodel surfactant, for variousforcing functions over a range oftemperatures and surfactantconcentrations

8. Advanced Gradient-Heating Facility:SL: LMSSpacehab/STS-95

9. Torque-VelocityDynamometer (TVD):SL: LMS

10. Visual andVestibularInvestigation System(VVIS):SL: Neurolab/STS-90

11. Advanced Protein-Crystallisation Facility:SL: IML-2 (2 units)

USML-2 (2units)LMS (2 units)

Spacehab-1 (1 unit)Spacehab/STS-95 (2units)

12. Glovebox:SL: USML-1

USML-2

13. MorphologicalTransition and ModelSubstances (MOMO):Spacehab: MM-6/STS-84Spacehab: STS-101

14. Facility forAbsorption andSurface Tension (FAST):Spacehab/STS-95

1 SL Standard Rack

180 kg + cartridges

Partly floor-mounted inSpacelab

130 kg

Centre-aisle mounted

160 kg

2 flights units exist

2 x 27 kg

Spacelab Double Locker size

54 kg

Self-standing drawer

65 kg

2 Spacehab Lockers

55 kg

Advanced high-performanceBridgman-type surface.Standardised cartridges. Cartridgesare stationary, furnace moves, tominimise microgravity disturbances.Max. temp 1400°C. Gradient 100ºC/cm

TVD measures force, torque andvelocity of various humanlimbs/joints in an adjustable andreproducible way, i.e. muscle-strength changes in orbit

VVIS’s most important element is a human off-axis rotating chair.Includes binocular 3D video eye-movement recording system.Centrifugal force reaches 1 g whenrotating at 45 rpm

Three crystallisation methodspossible: dialysis, interfacediffusion, vapour equilibrium. Eachmodel consists of 48 crystallisationreactors. 20 reactors observed/recorded by video prior to re-entry

Safe cabinet, in which partial gaspressures and temperatures arecontrolled. Provides illuminationand video recording

One experiment cell usedrepeatedly for solidification studiesat different temperature gradients(Bridgman furnace). The cellularstructure of the solidification frontsmonitored by video and recordedon internal digital tape recorder

Two independent experiment cells.Fluid/fluid and fluid/gas interfacescan be studied. Video system andimage processor tracks meniscusfor fluid-control loops andmeasures radius of droplet/bubble.Forcing frequency: 0.01– 600 Hz

Table 6.2 (cont’d) ESA Microgravity Multi-User Facilities for Spacelab/Spacehab

Figure 6.3.1. The Russian Bion/Foton retrievable capsule system, used by ESA for biologyand exobiology research


commercial basis. This started in 1990 with Foton-8 and continued in 1993 with Foton-9, in 1995 with Foton-10, in 1997 with Foton-11 and in 1999 with Foton-12.

For these flights ESA developed two further multi-user facilities:– Biopan for radiation biological, dosimetry and exobiological experiments– Fluidpac for various fluid-science experiments.

The technical capabilities of, and the missions and experiments performed with,Biobox, Biopan and Fluidpac, as well as the other autonomous experiments, are listedin Table 6.3.

The Biobox facility was flown later on theSpacehab/STS-95 mission in October1998, following its use on the Fotonflights. It is planned to re-fly it onSpacehab in 2002 (STS-107).

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Figure 6.3.2. The ESA Biobox andFluidpac payloads for the Russian Fotoncapsule

Table 6.3 ESA Multi-User Facilities and Experiments Flown on Bion/Foton Missions

Biobox:Incubator with 1g centrifuge, 24 experiment containers, temperature control in the range 6 - 37°C, telemetry/commandcapabilities, total mass 40 kg.

Biobox-1(Bion-10, 1992), Biobox-2 (Foton-10, 1995) and Biobox-3 (Foton-11, 1996) experiments:– Bones (Bion-10): Growth and mineralisation of fetal mouse bones in microgravity– Fibro (Bion-10, Foton-10 and -11): Morpho-physiological properties and differentiation of cell-culture fibroblasts under

microgravity– Oblast (Bion-10, Foton-10 and -11): Osteoblastic cells (cell culture from rat) in weightlessness: morpho- and biochemical

response– Marrow (Bion-10, Foton-10 and -11): Effect of microgravity on in-vitro cultures of pre-osteoblast cells and on MG-63

human osteosarcoma cells.

Biopan:Cylindrical pan-shaped container mounted on external surface of Foton, deployed in orbit and closed prior to re-entry toprovide exposure of biological specimens to measured levels of space/solar radiation, vacuum and microgravity. Surfacearea 1080 cm2, mass 30 kg. temperature control in the 15 - 25ºC range.

Biopan-1 (Foton-9, 1994), Biopan-2 (Foton-11, 1997), Biopan-3 (Foton-12, 1999) experiments:– Base (Foton-9 and -11): Base damage induced by cosmic radiation in cellular DNA– Shrimp (Foton-9 and -11): Radiation effects in gastrulae from the brine shrimp Artemia– Vitamin (Foton-9, -11 and -12): Radiation effects and efficiency of radio-protective substances in biological acellular systems– Mapping (Foton-9 and -11): Radiation measurements behind defined shieldings– Survival (Foton-9, -11 and -12): Effect of the harsh environment (of solar UV) on micro-organisms– Shutter (Foton-9 and -11): Biological UV dosimetry– Dust (Foton-9 and -11): Processing and stability of biomonomers in artificial dust grains– Dosimap (Foton-12): Dosimetric mapping– Yeast (Foton-12): Radiation damage in yeast: interaction of space-radiation components

Fluidpac:This instrument accommodates 3-4 experiments, for which it provides diagnostic interferometers, IR and CCD cameras withdata compression, a variety of sensors for in-situ measurements, and a Telesupport Unit for operations from the ground,scientific data transmission, and 5 Gbyte of data storage. Total mass is 185 kg. It handles 400 W, has a large volume of 1700 litres. It provides accurate ±0.1ºC temperature control in the range of 3 – 40ºC and good stability (±0.01ºC/hour)During the first flight of Fluidpac on 12 February 1999, the following three experiments were performed:– Magia: Marangoni-Grown Instabilities in an Annulus– Bambi: Bifurcation Anomalies in Marangoni-Bernard Instabilities– Tramp: Thermal Radiation Aspects on Migrating Particles.

Autonomous ESA-selected experiments flown on Bion/Foton missions:– Caraucos

Bion-8 and -9: Study of the effects of microgravity and HZE particles of cosmic radiation on embryogenesis of the stick insect– Dosicos

Bion-8 and -9: Radiation dosimetry inside and outside the spacecraft; radiation damage in plant seeds (lettuce seeds). Bion-10: Identification and quantification of incident radiation particles during orbital space flight

– SeedsBion-8 and -9: Biological effects of higher and lower ionising cosmic heavy particles in genetically variable (embryonic)plant tissuesBion-10: Analysis of chromosomal damage of marker lines in Arabidopsis seed by cosmic heavy particles, including protons

– FliesBion-9: Effects of microgravity and radiation on fruit-fly development, ageing, rate of mitotic recombination and adaptation to the space environmentBion-10 and Foton-10: Test of the metabolic hypothesis of accelerated ageing in space in Drosophila Melanogaster

– ProtodynBion-9: The effect of the microgravity environment on the regeneration of plant protoplasts

– KashstanFoton-7: Protein crystallisation in microgravity: HIV reverse transcriptase

– AlgaeBion-10, Foton-10 and -11: Changes in cell-division cycle of Chlamydomonas Monoica caused by microgravityFoton-12: Effect of microgravity on cell-cycle kinetics in the unicellar algae Chlamydomonas Monoica

– CloudBion-10: The impact of pre-flight gravity stress on in-flight fitness in Drosophila Melanogaster

– WolffiaBion-10: Radiation damage in Wolffia Arrhiza caused by heavy ions of cosmic rays

– BeetleFoton-10 and -11: Biological clocks of beetles: reactions of free-running circadian rhythms to microgravity

– StoneFoton-12 and IRDI-Demonstrator flight in 2000: Thermal processing of artificial sedimentary meteorites during atmosphere re-entry

– SymbioFoton-12: Plant-bacterial symbiosis in microgravity

The ESA life- and materials-science experiments performed on the Euromir ’94 missionare listed in Table 6.4

The Euromir ’95 mission was originally planned to last 135 days, but was laterprolonged to 179 days, with launch on 3 September 1995 and landing on 29 February1996. The ESA astronaut on this mission, Thomas Reiter, was not only trained as ascience astronaut, but also as flight engineer with prescribed responsibilities for Miroperations, including extravehicular sorties. This mission gave ‘western’ Europeanscientists their first opportunity to perform investigations of prolonged periods inweightlessness.


6.4 ESA Microgravity Experiments and Facilities Flown on Mir

At the beginning of the 1990s, several ESA Member States chose to strengthen theirinternational co-operation with Russia in space activities, as part the dramaticgeopolitical evolution that had just taken place. This was partly realised byestablishing bilateral research programmes, and also by sending French, German andAustrian astronauts to the Russian Mir space station in order to carry out research. AUK astronaut was also sent to Mir, although that mission was in the context of aprivately funded project.

In view of this changed political situation, the ESA Council in November 1992approved a Columbus Precursor Flight Programme, the main elements of which weretwo ESA missions to Mir in 1994 and 1995 (designated Euromir ’94 and ’95). The mainobjectives of these missions were:

(i) the flights to Mir and the experience obtained there by two ESA astronauts(ii) the preparation of the European space user community for the Space Station/

Columbus era by providing long-duration experiment possibilities (iii) the acquisition of experience in the operation of manned systems and experimentation

support areas.

Euromir ’94 was a 31-day mission, from 3 October to 4 November 1994, whichinvolved Ulf Merbold as the ESA astronaut. It included the uploading of a 110 kg ESApayload, and the downloading of 10 kg to be brought back to Earth in the Soyuzmanned transfer vehicle, together with the astronauts. The selection of experimentsfor Euromir ’94 took place in early 1993 and it was clear that, because of this tightschedule, no new research facilities could be developed in time. Therefore only existingexperimental equipment developed for previous missions, or Russian, French, Germanand Austrian hardware already onboard Mir, could be used.

The ESA experiments selected for Euromir ’94 were predominantly life-sciencesexperiments from the human-physiology field. 21 European and 1 US life-scienceexperiment were selected, of which six were ‘ground experiments’, i.e. requiring onlypre- and post-flight measurements. In addition, four materials-science experimentsand two technology experiments were selected and flown.

The four materials-science experiments that had planned to use the Russian CSK-1furnace already on-board had to be postponed due to its malfunctioning. The life-science experiments used either small ESA-provided hardware items, such as blood,urine and saliva kits, a cooler/freezer and a hematocrit centrifuge, or they were PI-provided small instruments, pharmaceutical drugs or onboard Mir instruments. Thetwo selected technology experiments were a crew PC and an ion-emitter experiment.

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Table 6.4 The Euromir ’94 Life- and Materials-Science Experiments

– Circadian Rhythm and Sleep– Fluid and Electrolyte Balance– Magnetic Resonance Spectroscopy and Imaging of Human Muscles (GE)– Radiation Health during Prolonged Spaceflight– Chromosomal Aberrations in Peripheral Lymphocytes of Astronauts (GE)– Fluid-Volume Distribution and Tissue Thickness– Effects of Changes in Central Venous Pressure on the Erythropoietic System (GE)– Spatial Orientation and Space Sickness – Posture and Movement– Spatial, Temporal and Mental Process/Cognitive Changes– Volume Regulation and Heart-Rate Variability– Changes in Mechanical Properties of Human Muscle as a Result of Spaceflight (GE)– Bone Mass and Structure Changes and Bone Remodelling in Space– Influence of Spaceflight on Energy Metabolism– Adaption of Basic Vestibulo-Oculomotor Mechanisms to Altered Gravity– Gastro-enteropancreatic Peptides– Non-Invasive Stress Monitoring in Spaceflight by Hormone Saliva Measurement– Otolith Adaptation to Different Levels of Gravity (GE)– Biomechanical and Bioenergetic Changes of Human Muscles (GE)– Osmo- and Volume Regulation in Man (Dynamic Response)– Immune Changes after Spaceflight– Eye Torsion Changes during Space-Adaptation Syndrome

• Liquid–Liquid Phase Separation in Glasses by Microgravity • Research on Bulk Metallic Glasses• Thermophysical Properties of Undercooled Melts• Reaction and Solidification Behaviour of In-Situ Metal Matrix Composite

GE = Ground Experiment

the broadband ultrasound attenuation in the bones. The accuracy and reproducibilityachieved for these two measurements – 0.3% and 2%, respectively – were sufficientto satisfy the analysis. Other experiment objectives were to determine in how fardrugs and specific exercises can counteract the effects of weightlessness. Figure 6.4.1shows the commercial clinical version of the Bone Densitometer spun-off from theEuromir ’95 BDM experiment.

- The Respiratory Monitoring System (RMS-2)

The first-generation respiratory monitoring system was developed for the D-2 Spacelabmission. A traditional gas analyser is based on a mass-spectrometer and requires ahigh vacuum in order to operate, making it a heavy and bulky instrument. Toovercome these undesirable (for spaceflight) features, a new gas-analysis technique,


The Call for Experiments for the Euromir ’95 mission resulted in the selection of 19 life-science, 8 materials-sciences, 10 technology and 4 space-science experiments. The life-and materials-science experiments are listed in Table 6.5.

For this long-term space mission, ESA developed two multi-user facilities: the BoneDensitometer (BDM) and the second generation of the Respiratory Monitoring System(RMS-2). The technical resources originally available to ESA for Euromir ’95 were 200kg of upload with the unmanned Progress transport vehicle, plus 10 kg of upload anddownload with the manned Soyuz TM vehicle. After the development of all of themicrogravity experiment hardware, including RMS-2 and BDM as major facilities, therequired ESA upload had increased from 210 kg to 367.4 kg and the (marginal)download from 10 kg to 22.6 kg. Since the Columbus Precursor Flight Programme hadpaid the Russians for the Euromir ’94 and ’95 missions on the basis of a firm fixedprice of 50 MEuro, and since the excess mass stemmed from the microgravityhardware, the additional 5 MEuro needed to cover the excess upload and downloadcosts was provided by the EMIR-1 programme. Looking back, this was an extremelycost-effective investment for a six-month duration manned space mission, particularlyas both multi-user facilities (BDM and RMS-2) were later developed into very lucrativeterrestrial ‘spin-offs’, as reported in Chapter 3.

The two Euromir missions certainly fulfilled their political, technical and operationalobjectives. Their scientific returns were also very satisfactory, given that the downloadcapability was extremely limited and that none of the experimental facilities couldtherefore be brought back. The data-transmission capabilities were also limited: it wasnot possible to transmit high-speed experiment data rates, nor was full orbitalcoverage achieved.

- The Bone Densitometer (BDM)

This was the first instrument capable ofmonitoring bone-density changes inastronauts during the actual mission.The new feature of the BDM was that itwas not an X-ray instrument, as in anormal bone densitometer, but anultrasound measurement device, whichpresents no hazard to the crew due torepeated exposure and requires noradiation shielding. To evaluate the lossof mass or the demineralisation inweight-bearing bones (the astronaut’sheel was used), the BDM measured thespeed of sound (transmission delay) and

454 sdddd SP-1251

Table 6.5 The Euromir ’95 Life- and Materials-Science Experiments

– Influence of Microgravity on Renal-Fluid Excretion in Humans– Non-Invasive Monitoring of Drug Metabolism and Drug Effect during Prolonged Microgravity– Effect of Otolith Input on Ocular and Neck Reflexes and Perceived Vertical – Eye-Torsion Change Correlation to Space-Adaptation Syndrome– Chromosomal Aberrations and Repair in Peripheral Lymphocytes (GE)– Radiation Health during Prolonged Spaceflight– Influence of Gravity on Preparation and Execution of Voluntary Movement (GE)– Effect of Microgravity on the Bioenergetic Characteristics of Human Skeletal Muscles (GE)– Changes in Mechanical Properties and Reflex Responses in Human Muscles (GE)– Human-Muscle Magnetic-Resonance Spectroscopy and Imaging (GE)– Central Venous Pressure during Weightlessness– Cardiovascular-, Pulmonary Control and Pulmonary Gas Exchange (Rest + Exercise)– Pulmonary Function in Microgravity – Regulation of Cardiovascular Responses to Exercise in Humans– Interstitial Fluid Balance under Microgravity and Pulmonary Mechanics– Influence of Vitamin-K on Bone Metabolism– Bone Mass and Structure Measurement with BDM and Bone-Stiffness Measurement Device– Effect of Venous Pressure on Bone Mineral Density in Weightless Conditions– Mechanical Stimulation to Prevent Loss of Bone Mass using Heel-Strike Transients

• Equi-axed Solidification of Al• Reaction and Solidification Behaviour in Metal-Matrix Composites• Specific Heat of Undercooled Melts• Investigation of Chemical-Vapour Transport • Liquid-Liquid Phase Separation in Glasses• Thermosolutal Convection in Ge-Si• Metallic-Glass Research• Casting of Hypermonotectic Alloy

GE = Ground Experiment

Figure 6.4.1. The ESA Bone Densitometerused on the Euromir ’95 mission resultedin development of this spin-off version fornormal clinical use on Earth


namely the photo-acoustic method for poly-atomic gases (developed and patented byBruel and Kjaer, Denmark) was used, supplemented by a magneto-acoustic method fordetecting oxygen. This new method allowed a drastic reduction in terms of mass,volume and power needs, but had the potential disadvantage of not being able tomeasure all gases. For the Euromir ’95 experiments, it was acceptable that the RMS-2would measure continuously the oxygen, carbon-dioxide, nitrous-oxide andhexafluoride concentrations in therespired gases. In addition to the basicgas analyser, the RMS-2 on Euromir ’95included an ECG module, a continuousblood-measurement device to monitorthe subject’s physical condition, aRespiratory Inductance Plethysmograph(RIP), which measures the movements ofthe thorax and the abdomen duringnormal breathing, and PI-providedinstruments: handgrip dynamometer,infrared pulso-oximeter and haemo-globin photometer. The complete RMS-2instrument package, including a consider-able amount of consumables such as480 litres of experiment-specific gas in apressurised system (needed for the longmission duration), had a mass of 130 kg.

The RMS-2 experiment programme alsoincluded pre- and post-flight Baseline Data Collection (BDC). This required that the crewrepeated the measurements after the mission, to study the re-adaptation to gravityfollowing a long space mission.

6.5 Summary of Missions, Facilities and Experiments

Table 6.6 lists all missions on which ESA payloads have flown (apart from the short-duration flight opportunities offered by sounding rockets, parabolic aircraft flights,and drop tubes/towers); it therefore includes Spacelab, Bion/Foton, Eureca, Euromir’94 and ’95 and Spacehab, together with the facilities flown, and the numbers of ESAexperiments in the physical and life sciences performed on each of these missions.Slightly more than half of the total of 412 experiments are life-science related.

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Figure 6.4.2. The Respiratory MonitoringSystem, used on the 179-day Euromir ’95mission to monitor the cardiovascularsystem and pulmonary performance

Table 6.6. The ESA Physical- and Life-Sciences Experiments performed on Spacelab, Bion/Foton,Eureca, Euromir ’94 and ’95 and Spacehab

Mission/Year Physical Life Subtotal Experiment Facilities UsedSciences Sciences

1. Spacelab Missions1.1 SL-1 (1983) 36 8 441.2 D-1 (1985) 6 20 261.3 IML-1 (1992) 4 16 20 See Table 6.11.4 D-2 (1993) 9 19 281.5 IML-2 (1994) 25 18 431.6 USML-2 (1995) 14 - 141.7 LSM (1996) 27 5 321.8 Neurolab (1998) - 7 7

Subtotal Spacelab 121 93 214

2. Bion/Foton Missions2.1 Bion-8 (1987) - 3 3 Stand-alone Experiments2.2 Bion-9 (1989) - 5 5 Stand-alone Experiments2.3 Foton-7 (1991) 1 - 1 Kashtan (Protein Cryst. Fac.)2.4 Bion-10 (1992) - 9 9 Biobox2.5 Foton-9 (1994) - 7 7 Biopan2.6 Foton-10 (1995) - 6 6 Biobox2.7 Foton-11 (1997) - 13 13 Biopan, Biobox2.8 Foton-12 (1999) 4 7 11 Fluidpac, Biopan, Agat Furnace

Subtotal Bion/Foton 5 50 55

3. Eureca (1993) 22 6 28 AMF, SGF, PCF, MFA, ERA

4.1 Euromir ’94 (1994) 4 21 25 Freezers, Blood Kit4.2 Euromir ’95 (1995) 8 18 26 RMS-2, BDM, Blood Kit

5. Spacehab5.1 SH1 (1993) 10 - 10 APCF5.2 SH/MM3 (1996) - 8 8 Biorack5.3 SH/MM5 (1997) - 7 7 Biorack5.4 SH/MM6 (1997) 1 8 9 Biorack, MOMO5.5 SH/STS-95 (1998) 26 3 29 AGHF, APCF, FAST, MOMO,

Biobox5.6 SH/STS-101 (2000) 1 - 1 MOMO (Morphological

Model Substances)Subtotal Spacehab 38 26 64

Total No. of Experiments 198 214 412

* PS = Physical Sciences. LS = Life Sciences.

The major findings of the life- and physical-sciences experiments are presented in thediscipline contributions in Chapter 2. The annual number of publications in both lifeand physical sciences under microgravity conditions has increased strongly over thelast 15 years (by a factor 3) and the so-called ‘impact factor’, a measure of the qualityof the journals in which the publications have been accepted (from the journalCitations Reports issued by the Institute for Scientific Information), has also stronglyincreased (by a factor 3.5 over the last 15 years).

6.6 Short-Duration Flight Opportunities

From the start of Phase-1 of ESA’s Microgravity Programme, short-duration flightopportunities were always a solid programme component, amounting to about 25%of the financial envelope. They started in May 1982, with ESA’s participation in theTexus-6 sounding-rocket flight. Some 25 experiments were performed between 1982and 1986. In 1987, during Phase-2 of the Programme, the frequency of ESA sounding-rocket flights was doubled to two per year. This increase was introduced tocompensate for the six-year hiatus in Spacelab flight opportunities caused by theChallenger accident. ESA provided further short-duration flight opportunities from1984 onwards with the introduction of parabolic aircraft flights, supplemented laterwith research opportunities in the drop tube at Grenoble (F) and the drop towers atBremen (D) and near Madrid (E).


Table 6.7 shows the annual distribution of ESA-selected experiments performed onthese missions, in the period 1983 – 2000, and the planned experiments and missionsfor the years 2001 and 2002.

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Table 6.7. Annual Distribution of ESA-Selected Experiments performed on Spacelab, Bion/Foton,Eureca, Euromir ’94 and ’95 and Spacehab

Year No. of Expts. Mission1983 44 Spacelab-1 (SL-1)1984 - -1985 26 Spacelab D-11986 - -1987 3 Bion-81988 - -1989 5 Bion-91990 - -1991 1 Foton-71992 29 Spacelab IML-1, Bion-101993 66 Spacelab D-2, Eureca, Spacehab-11994 75 Spacelab IML-2, Foton-9, Euromir ’941995 45 Spacelab USML-2, Foton-10, Euromir ’951996 40 Spacelab LMS, Spacehab MM31997 29 Foton-11, Spacehab MM5 and MM61998 36 Spacelab Neurolab, Spacehab STS-951999 12 Foton-122000 1 Spacehab/ STS-101 (MOMO)

2001 29 Spacehab /STS-107: ARMS(8), Biopack(7), Biobox(4), (planned) (LS:21+PS:8) Osteo(2), APCF(6), Fast(2)2002 30 Foton M1: Biopan(4), IBIS(3), Stone(1), Fluidpac(4), (planned) (LS:23+PS:7) Agat Furnace(3) (mission to be confirmed).

Spacehab-R2: ARMS(8), Biopack (7)

Total incl. 471 Of which 258 are life-sciences and 213 physical-sciencesplanned experiments

LS = Life Sciences, PS = Physical Sciences.

Figure 6.5.1. Annual distribution of ESA microgravity experiments conducted in space,including the six-year hiatus in flight opportunities after the Challenger accident

By mid-2000 ESA had supported flight opportunities on 41 sounding-rocket flights.With the help of industry, the Agency has developed a multitude of experimentmodules and has frequently upgraded the service modules providing the telemetrydown-link and telecommand up-link for the individual experiment modules.

Most of the flights have been performed within the framework of the Texus project,which was originally initiated (in 1976) by DLR, but later industrialised by thecompany MBB/ERNO-DASA. The Maser project was started in 1987 by the SwedishSpace Corporation (SSC) and its last three missions were used exclusively by ESA on acommercial basis. Maxus, a joint venture between DASA and SSC, is also used by ESAon a commercial basis. The Mini-Texus programme was initiated by DASA in 1993, toprovide cheaper flight opportunities for those investigations that can be performed inabout 3 minutes of microgravity. This is of particular interest for combustionexperiments. The launch campaigns for all four types of rocket take place at Esrange,near Kiruna in northern Sweden, as this launch site allows land recovery of thescientific payload.

By mid-2000, 38 Texus flights had taken place, of which 25 were used by ESAexperiments (the others were used solely by DLR and SSC). A further 8 Maser flights, 4 Maxus flights (Maxus-1 had a rocket failure) and 4 Mini-Texus flights have also takenplace. The ESA experiments performed on each of these rocket missions, together withtheir scientific themes, are listed in Tables 6.8 (Texus), 6.9 (Maser), 6.10 (Maxus) and6.11 (Mini-Texus).


- Sounding-Rocket Flights

The sounding-rocket activities, which presently consist of the Texus, Maser, Maxusand Mini-Texus projects, have represented by far the largest element of the short-duration flight opportunities:– Texus (Technologische Experimente unter Schwerelosigkeit): 360 sec of microgravity,

about 250 kg of scientific payload– Maser (Materials-Science Experiment Rocket): 360 sec of microgravity, about 250 kg

of scientific payload– Maxus (name derived from Maser and Texus): about 780 sec of microgravity, about

450 kg of scientific payload– Mini-Texus (using a smaller rocket, but the same payload diameter as Texus): about

180 sec of microgravity, 100 kg of payload

The rocket missions provide reasonably good microgravity levels (better than 10-4g),and use autonomous experiment modules developed for ESA or DLR by industry.Maxus can carry up to five experiment modules, Texus/Maser three to five modules,and Mini-Texus one or two modules, always in addition to a service module supplyingdata management via real-time telemetry/commanding and TV modules providingreal-time video observation. The scientists are able to interact with their experimentsduring the flight (tele-science), a featurethat has been available since 1983.

Sounding rockets provide reliable andfrequent flight opportunities, with ESAcurrently performing typically two flightsper year. They offer a short-preparation/turn-around time of 1.5 – 2.5 yearsbetween experiment selection and flight.In addition, the safety and documentationrequirements for the experiments arevery much lower than those for payloadson manned missions. It has turned outthat sounding-rocket experiments arenot only very useful as precursorexperiments for later Spacelab/Spacehab and Mir missions or for theverification of the functioning oftechnical designs in low gravity, but theyalso provide several sub-disciplines withresults that constitute a high scientificreturn in themselves.

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Figure 6.6.1. Launch of a Maxus soundingrocket from Esrange, in Sweden

Table 6.8 cont’d . Texus Sounding-Rocket Flights Carrying ESA Experiments

Launch Flight No. ESA Research Topics of Experiments PerformedExpts.

March 2000 Texus-37 1 Critical velocities in open capillarity flow

April 2000 Texus-38 3 Droplet combustion evaporation. Flame spreading and forced flow convection.Signal transduction in osteoblasts

70 Of these 70 experiments, 4 were from the life sciences


Table 6.8 Texus Sounding-Rocket Flights Carrying ESA Experiments


May 1982 Texus-6 4 Metallic composites. Diffusion in cast iron. Striations in germanium. Eutectic solidification.

May 1983 Texus-7 3 Metallic components with particles, immiscible AlPb alloys, single crystals of CeMg3.

May 1983 Texus-8 2 Liquid-phase sintering, surface-tension/Marangoni effects

May 1984 Texus-9 4 Metallic composites, containerless solidification, thermal Marangoni convection, surface-tension minimum

May 1984 Texus-10 4 Critical point of H2O. Ga-doped Ge crystal growth. Tungsten composites.Floating-zone injection

April 1985 Texus-11 1 Phase separation at critical point

June 1985 Texus-12 4 Liquid bridge. Critical point of H2O. Rare-earth crystal growth. Ge crystal growth

April 1986 Texus-13 3 Salt crystallisation. Repeat of Marangoni experiment of Texus-8. Repeat of critical-point experiment of Texus-11

May 1987 Texus-14 B 6 Containerless alloy undercooling. Fluid-dynamics expt. Solidification of ZnBi Metal composites, dispersions, Ge crystal growth

May 1988 Texus-17 3 Ultrasound adsorption in salts. Colloid chemistry. Role of gravity indorsal-ventral axis of amphibian embryos

May 1988 Texus-18 1 Freezing of long liquid column

Nov. 1988 Texus-19 5 Tungsten-composite sintering. Refractive-index change by ion exchange. Electrostatic positioning. Marangoni experiment reflight

Dec. 1988 Texus-20 1 Metal matrix composites

April 1989 Texus-21 2 Benard-Marangoni instabilities in circular and rectangular cells

Nov. 1989 Texus-23 3 Critical Marangoni flow. Rotational instabilities of liquid columns. Coagulation of dispersions

May 1990 Texus-25 1 Density and temperature relaxation near the critical point of CO2

May 1990 Texus-26 1 Liquid-phase sintering of tungsten composites

Nov. 1990 Texus-27 6 Remelting of Fe-C-Si alloys. Heat-storage model. Liquid-phase sintering. Pressures in supercritical salt solutions. Visualisation of electrophoresis. Gravity’s role in spatial orientation of biological cells

Nov. 1991 Texus-28 2 Reflight of Texus-27 electrophoresis expt. Reflight of orientation of biological cells

Nov. 1993 Texus-31 4 Wetting of GaInSb. Nucleation bubble growth/evaporation/condensation. Coagulation of suspensions. Marangoni instabilities

May 1994 Texus-32 2 Marangoni convection by evaporation. Differential wetting of GaInSb melts

Nov. 1994 Texus-33 3 Acceleration of liquid columns. Convection instabilities in phase separation of mixed fluids. Adsorption and surface tension

March 1996 Texus-34 1 Reflight: Interactive Marangoni convection

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Table 6.9 Maser Sounding-Rocket Flights Carrying ESA Experiments


March 1987 Maser-1 5 3D-Marangoni convection. Thermo-capillarity. Drop motion. Thermal conductivity, meniscus stability if immiscible metals

Feb. 1988 Maser-2 7 3D Marangoni convection. Thermo-capillarity. Drop motion. Bridgman growthof Ga-doped Ge (2 expts). Directional solidification of immiscible alloy ZnPb. Adhesion of metals on ceramics. Precipitation in Zn-Bi alloys

April 1989 Maser-3 8 Metal-matrix composites. Particle agglomeration. Thermo-capillarity. Drop motion. Protein crystal growth. Membrane functions in green algae. Regulation of cell growth (growth-factor receptor for interaction). Binding of Concavalin A to Lymphocytes. Dorsoventral axis development in amphibian embryos

March 1990 Maser-4 5 Measurement of interfacial tensions. Orientation of DNA molecules during electrophoresis. Fertilisation of urchin eggs. Embryogenesis lymphocytes in microgravity. Regulation of cell growth and differentiation

April 1992 Maser-5 6 Wet satellite model. Solutal Marangoni effect. Marangoni effect due toevaporation. Refl. of expt.: Fertilisation of urchin eggs and embryogenesis. Plasma-membrane fusion in human fibroblasts. Nuclear response to protein. Kinare C signal transduction

Nov. 1993 Maser-6 5 Solutal Marangoni effect. Interaction on Marangoni migration. Cleavage stagedevelopment of urchin eggs after microgravity exposure. Development of Xenopus eggs fertilised in space. Cell-growth regulation and differentiation

May 1996 Maser-7 7 Enzyme catalysis. Liquid-phase epitaxial growth of SiC. Pool boiling with/without electric field. Signal transduction mechanisms in microgravity inimmobilised neuroendrine cells. In-vivo culture of differentiated functional epithelial follicular cells from the thyroid gland

Jan 1998 Maser 1 Convective boiling and condensation of ammonia in microgravityTech. Flight

May 1999 Maser-8 4 Cosmic-dust aggregation. Thermal-radiation forces in non-stationary conditions.Pool boiling with/without electric fields. Jet growth motions in aerosol



Table 6.10. Maxus Sounding-Rocket Flights Carrying ESA Experiments


Nov. 1992 Maxus-1B 7 Directional solidification of LiF-LiBaF3 eutectics. GaAs floating-zone (Maxus 1 growth. Floating-zone processing of fluoride glasses. Oscillatory rocket failed) Marangoni convection. Electrophoretic orientation.

Marangoni convection. Lymphocyte experiments

Nov. 1995 Maxus-2 8 Marangoni instability in liquid containers. Marangoni instability near the critical-point. Continuous-flow electrophoresis. Influence of acceleration on spatial orientation of paramecium and loxodes lymphocytes. Behaviour of liquids in corners and at edges. Instability of multi-layered systems

Nov. 1998 Maxus-3 5 Pulsation and rotating instabilities in oscillatory Marangoni flows. Electrodynamic distortion during electrophoresis. Perception and ligual transduction in microtubule solution. Mechanism of gravitactic signal perception. Experiments in Chara Phizoids


Table 6.11. Mini-Texus Sounding-Rocket Flights Carrying ESA Experiments


May 1994 Mini-Texus 2 2 Marangoni Benard instability. Freon boiling experiment

May 1995 Mini-Texus 3 1 Influence of forced convection on flame-spreading processes over solid fuels

Feb. 1998 Mini-Texus 5 1 Piston effect in model fluids submitted to an oscillatory acceleration

Nov. 1998 Mini-Texus 6 1 Laminar-diffusion flames established over a flat fuel surface

5 No life-sciences experiments

Table 6.12. Annual Distribution of ESA Experiments on Sounding Rockets

Year Texus Maser Maxus Mini-Texus Total 1982 4 41983 5 51984 8 81985 5 51986 3 31987 6 5 111988 10 7 171989 5 8 131990 8 5 131991 2 - 21992 - 6 7 131993 4 5 91994 5 2 71995 - 8 1 91996 1 7 81997 - -1998 - 1 5 2 81999 - 4 42000 4 4

Total 70 expts. 48 expts. 20 expts. 5 expts. 143 expts.

Table 6.12 shows the annual distribution of all microgravity experiments on soundingrockets sponsored by ESA.

It clearly shows how ESA increased (at least doubled) the average number ofexperiments each year after the Challenger accident in 1986. A total of 143 ESAmicrogravity experiments were performed on sounding rockets between May 1982and mid-2000, of which about half used the Texus flight opportunities. 25 of these 143experiments were from the life sciences.

A sounding rocket can accommodate a number of experiments, not necessarilyprovided by the same space agency. In particular, many Texus flights (consisting of 3–5 experiment modules) were shared between DLR and ESA. The costs are also thenshared pro-rata, according to the respective payload masses.

In total, ESA has flown about 6 tons of scientific payloads and associated servicemodules on sounding rockets, conducting many highly successful experiments in thefields of diffusion, electrolysis, interface phenomena, alloy solidification,crystallisation, critical-point research, combustion and biology. The results of theseexperiments have been published in the ESA Special Publication series: ESA SP-1132for the physical-science experiments and ESA SP-1206 for the life-sciencesexperiments, available from ESA Publications Division.

- Drop Towers and Drop Tubes

Drop tubes and drop towers are ground-based research facilities in which up to10 sec of free-fall conditions can beachieved. Such facilities are being usedfor microgravity research in the USA,Japan and Europe. In line with the ESAMicrogravity Programme’s objective ofproviding practical opportunities forconducting experiments under low-gravity conditions, it offers experimenttime free of charge for selectedexperiments at the drop tube in Grenoble(F) and at the drop towers in Bremen (D)and Madrid (E).

The 47 m-high drop tube in Grenoble (F)provides about 3 sec of microgravity at alevel of 10-8g. It has an internal diameterof 20 cm and is operated under ultra-high vacuum, which allows containerless

processing of metal droplets forsolidification studies, nucleationresearch, etc.

The drop tower in Bremen (D) is a multi-purpose facility for short-durationcombustion, fluid-sciences and bio-technology experiments. It is anevacuated system, 110 m high and 3.5 min diameter, which provides 4.7 sec ofmicrogravity (10-5g) for experimentpackages of up to 170 kg. To double themicrogravity duration, the tower ispresently being fitted with a catapultsystem delivering a controlledacceleration. During its 10 years ofexistence, this drop tower has been usedfor about 3000 free-fall experiments. Anaverage of about 30 drops are performedper experiment.


- Parabolic Flights on Aircraft

Aircraft parabolic flights provide up to 20 seconds of low gravity (about 10-2g). Theyare used to conduct short microgravity investigations in the life and physical sciences,to test instrumentation, and to train astronauts prior to a space flight. A campaigncomprises typically three flights, each flying 30 parabolas.

In the past, ESA used various aircraft for precursor investigations and for the functionaltesting of Spacelab, Mir and Spacehab experiments:– KC135 (provided by NASA): 1984 – 1989, 6 campaigns in the USA, and 1996,

1 campaign near Bordeaux– Caravelle 234 (provided by CNES/Novespace):

1989 – 1995, 15 campaigns in Bretigny near Paris– Ilyushin IL-76MDK (provided by Russian Space Agency):

1 campaign in July 1994 near Berlin in preparation forthe Euromir ’94 and Euromir ’95 missions

– Airbus A300 (CNES/Novespace): Since October 1997, with an average of 2 flight campaigns per year for ESA, near Bordeaux

The main advantages of parabolic flights are their short turn-around times of a fewmonths, their low cost and their geographical proximity within Europe. The possibilityfor direct intervention by the investigators on board the aircraft is also a majoradvantage. By mid-2000, ESA’s Microgravity Programme had supported 26 parabolicflight campaigns, during which a total of 360 experiments were performed.

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Figure 6.6.2. The Airbus A300 during a parabolic-flight manoeuvre, which creates low-gravity conditions lasting about 20 seconds (courtesy of Novespace)

Figure 6.6.3. The drop tube in Grenoble (F),which provides 3 sec of weightless, free-fallconditions for solidification experiments(courtesy of CENG-Grenoble)

Figure 6.6.4. The Bremen drop tower,which can accommodate free-fallexperiment packages of up to 170 kg(courtesy of ZARM)

– The Exobiology and Radiation Assembly (ERA), for exposing about 1000 specimensto selected features of the space environment.

Due to financial limitations, the originally planned botany facility with a closedecological life-support system could not be developed for the first Eureca mission.

The Eureca platform had a payload mounting surface of 4.3 m by 2.2 m. The totalmass of the platform was 4.5 tons, of which 1 ton was available for payload. The in-orbit hardware consisted of a core payload of the above listed five multi-user facilities,and a number of microgravity, space-science and technology add-on experiments. TheESA core payload was made up of processing chambers for crystal growth (inorganicand protein crystals) and furnaces for metallurgical experiments, and it allowed thestudy of the impact of the space environment – solar and cosmic radiation,weightlessness and vacuum – on organic molecules, membranes, bacterial spores,etc. The Eureca core payload’s technical features and the experiments using the multi-user facilities of the core payload are summarised in Table 6.13.

The Eureca programme, which was originally planned to consist of a series of missions,was terminated after the first 11-month flight (launched 31 July 1992). Despite stronginterest from the relevant user community, and although excellent microgravity levels(10-5 – 10-6g) were achieved during that first mission, it proved impossible to get theparticipating ESA Member States to agree to any re-flights of the platform.


The drop tower at INTA, near Madrid, is a 21 m-high facility, which provides 2.1 sec offree-fall conditions. As the fall occurs in the open air, the experiments are subject toaerodynamic drag. This can be avoided by using a drag-shield technique, whereby theexperiment is released to fall freely inside an all-enveloping dropping capsule.

The experiment-support services provided at the drop towers/tube are already of ahigh technical standard and are continuously being upgraded.

6.7 The European Retrievable Carrier (Eureca) and Its Payload

The ESA Microgravity Programme’s Phase-1, and later EMIR-1, provided microgravityresearch opportunities with durations ranging up to a maximum of 17 days onSpacelab missions. Analysis of the requirements of the experiments being proposedrevealed that a number of them called for:– Longer missions (especially for gravitational biology research and multi-generation

plant growth). – Better microgravity levels than were achievable on Spacelab (10-4g) missions. The

movements of astronauts induced considerable disturbances in the microgravityenvironment on Spacelab.

In 1980, therefore, ESA began studying a re-usable free-flying platform, initially calledMireca (Microgravity Retrievable Carrier), which would be launched by the Shuttle intoa 250 km orbit, boosted to a 500 km-altitude orbit by its own propulsion system, andthen retrieved again by the Shuttle after a 6 – 9 month stay in orbit. The name Mirecawas subsequently changed to Eureca, to make it clear that investigations from otherdisciplines could also be flown.

Following a Call for Experiments, which was extended to all other disciplines such asspace science, applications and technology, the Eureca programme was approved in1982 and the first mission was scheduled for 1987. Unfortunately, due to theChallenger accident and the subsequent interruption of Shuttle flights, Eureca’smaiden flight had to be postponed until 1993. Due to the large interest from thevarious microgravity disciplines, the Eureca development programme also includedfive microgravity multi-user facilities:– The Automatic Mirror Furnace (AMF), for crystal growth of semi-conductors.– The Solution-Growth Facility (SGF), for low-temperature crystal growth from the

solution.– The Protein-Crystallisation Facility (PCF), for protein crystallisation in 12 growth

reactors.– The Multi-Furnace Assembly (MFA), using 10 different furnaces for metal and alloy

solidification studies.

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Figure 6.7.1. The Eureca retrievable carrier, which carried a 1 ton experiment payload andwas launched and retrieved by the Space Shuttle

The main reasons why reflights were not approved were:– The Shuttle launch and retrieval costs had increased dramatically after the

Challenger accident in 1986, compared with the first Eureca flight, for which theESA/NASA Shuttle-launch agreement had been concluded in 1983/84.

– Due to the Shuttle-imposed delay of more than 5 years on the first Eureca mission,the latter’s development costs had considerably exceeded the original financialenvelope. The Eureca microgravity core payload, however, represented less than15% of the overall Eureca programme costs.

– Eureca was, to a certain extent, seen as a predecessor of the Columbus Free-FlyingLaboratory. However, the financial limitations that ESA’s Member States imposedon the Columbus Programme led to the Free-Flying Laboratory being deleted in theearly 1990s.

From a scientific point of view Eureca’s first mission was a great success. It alsoincreased European technical know-how in retrievable free-flying satellites, theirintegration, fast disassembly after flight, and mission operations and, last but notleast, it reinforced international co-operation.


Multi-UserFacility

AutomaticMirror Furnace, AMF

Solution-Growth Facility, SGF

Protein-CrystallisationFacility, PCF

Multi-Furnace Assembly, MFA

Exobiology and RadiationAssembly, ERA

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Scientific Use

Vapour crystal growth of II-VI semiconductorsCdSe, CdTeSolution crystal growth of II-VI semiconductorsCdTe with Travelling Heater Method (THM)THM solution growth of III-V semiconductors:InP, Ga0.8 Al 0.2 SbTHM growth Pb1-x Snx Te compoundsSolution growth of ternary sulphides by THM: Ag Ga S2THM growth of Ca In2 Te4Solution growth of Ga Sn (In)

Formation of amorphous tricalcium phosphate by solute diffusion crystal growth of CaCo3Synthesis of Zeolite crystalsSoret diffusion-coefficient determination inbinary organic mixtures and electrolytesolution

12 independently controlled low-temperature solution-growth experiments of differentproteins in 12 reaction chambers. Proteinsinclude: Lysozyme, Beta-Galactosidase,Rhodopsin, Plasminogen, Fibrogen,Alpha Crustacyanime, tRNA, Asp/AspartittRNA Synthethase Complex, BacterioRhodopsin.

5 experiments in solidification, diffusion andcrystal growth: liquid-phase sintering, Ostwaldripening and diffusion, thermo-migration inliquid alloys, Pbx Sn1-.x Te and GaAs vapourgrowth, wettability of ceramic materials

Exposure of biological specimens to the spaceenvironment.Interaction of HZE atomic nuclei with tissues.Exposure of spores and organic material to thespace environment, effect of UV radiation onmolecule formation and destruction,measurement of the composition of thecosmic radiation in the Eureca orbit,inactivation and mutant induction by solarirradiation

Technical Features

Mass: 162 kg, incl. the 23 cartridges processed. Typical process temperature: 1000ºC (dependson sample)

Furnace consists of ellipsoidal cavity withhalogen lamp at one focus and the sample tobe processed at the other. The focussing of the lamp’s radiation melts the samples at atransverse section. By slowly pulling thesample cartridge out of the furnace, directional solidification is achieved. For homogenous temperature distribution, thesample is slowly rotated

Mass: 75 kg. Consists of 4 reactors, operating in controlled temperature range 35º – 90ºCindependently (± 0.1ºC)

There are 3 isothermal reactors and 1 Soretdiffusion reactor, consisting of 20 tubes inwhich thermal gradients are applied

Mass: 145 kg. Temperature control: 0º – 25ºC.Growth activation by connecting proteinchamber with salt chamber via a bufferchamber in which crystallisation occurs. At theend of the growth process, connecting growthchamber with fourth reservoir containingfixation salt increases the salt concentration. In-flight video observation and interaction with experiments is possible

Mass: 160 kg. Sequencial operation of 12furnaces, due to power limitations. MFAconsists of 12 furnaces, processing 33 samplesfor 5 experiments. Total processing time in orbit is 2 months. Temperature control in range up to 1000ºC. 6 single-zone furnaces, 4 three-zone furnaces, 2 isothermal furnaces

Mass: 57 kg. ERA consists of deployable andfixed experiment trays containing biologicalobjects such as spores, seeds or eggs,alternated with radiation and track detectors.The periods of exposure are predetermined by the PIs and are controlled by means ofshutters. Different space-radiation componentsare selected using optical band-pass filters

Table 6.13 The Eureca Core Payload, with Its Five ESA Multi-User Facilities


6.8 Future Experiments and Microgravity Application Projects

- Life Sciences

The concept of Topical Teams (TT) for the identification and definition of researchprogrammes and related experiments was already mentioned in Section 3.3.4. Inorder to prepare the future European life-sciences activities, ESA originally set up 10TTs, of which five were dedicated to space biotechnology/bioengineering subjects.

Since 1996, ESA has been participating, together with other ISS Partners and nationalspace agencies, in issuing international Life-Sciences Research Announcements(LSRAs) on an annual basis. These international, mainly ISS-related announcementshave resulted – after review, analysis and rating of the submitted proposals – in 84basic-research programmes being selected. In addition, 27 life-sciences MicrogravityApplication Projects (MAPs) from Europe have been selected by ESA. Non-spaceindustry participates in these MAPs in different ways and with different levels ofcontribution. The degree to which ESA provides financial support to selected MAPsdepends directly on the degree to which a research proposal is consideredapplications-oriented (from 0% for purely basic research, to 100% of an allocatedmaximum annual amount for a dedicated industrial applications-oriented researchproject). Financial support is provided by ESA only to the non-industrial partners in aproject, with industry providing additional contributions in kind or in cash. Experienceshows an average contribution by ESA of about one third of the total value of a project.

Not all of the experiments related to these basic-research and MAP projects involve anISS flight opportunity; they cover the whole range of precursor and preparatorystudies extending from ground-based bed-rest investigations to short-durationmicrogravity experiments, involving drop towers, parabolic aircraft flights andsounding-rocket flights. Experiment opportunities on Spacehab missions (7–16 days)using life-sciences facilities such as the ARMS (Advanced Respiratory MonitoringSystem), Biobox, Biopack, etc. are also required. Although the routine use of ISSfacilities will only become available in several years’ time (2005), a number of researchprogrammes are already requesting the use of ISS laboratories, in addition to otherearlier flight opportunities. Also, a number of exobiology experiments have beenselected for flight on a Mars-Lander mission.

- Physical Sciences

For the physical sciences also, special Topical Teams (TTs) are being formed, with 16already active at the end of 2000, as a result of earlier calls and selections. TheAnnouncement of Opportunity (AO) for research-programme proposals released byESA in 1998 and covering the fields of physical sciences and biotechnology resulted in68 proposals being selected, 21 of which are financially supported by ESA as MAPs,

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Table 6.8.1. Future Basic-Research and MAP Experiments in the Life Sciences

Flight/Research Facility* Flight No. of No. of Total Opportunity Year Basic MAP No. of

Expts. Expts. Expts.

Ground-Based Research Bed rest - 11 1 12

Sounding Rockets Maser-9 2001 2 1 3Maxus-5 2002 2 - 2Maser-10 2003 3 - 3

Spacehab:STS-107 Biobox-5 2002 4 - 4STS-107 ARMS 2002 8 - 8STS-107 Biopack-1 2002 8 - 8STS-107 Osteo 2002 - 2 2

ISS Increments 1-2, Dosimeter, Mapping 2001 1 7 8STS-102

ISS/US Laboratory Human Research Facility 2001/03 5 1 6+ PI Equipment EMCS 2003 5 2 7MARES/PEMS/HGD 2003 - 1 1Animal Research. Facility TBD 1 - 1

Shuttle Missions to the ISS MAP-supplied dedicated TBD - 7 7equipment, like sensors, etc.

ISS/Columbus Laboratory Biolab 2005/6 1 1 2EDR 2005/6 - 3 3EDR-BMTC TBD - 3 3

ISS TBD (recent MAPs) TBD (not EPM, Human TBD - 8 8(probably US Laboratory or Research Facility, partlyColumbus Laboratory) ground expts.)

ISS Externally Mounted Expt. Expose 2003/4 8 - 8

Matroshka 2003 4 - 4

Total 63 37 100

* Technical descriptions of the facilities can be found in Sections 5.2, 6.2, 6.3 and 6.6.

Tables 6.8.3 and 6.8.4 provide details about the life- and physical-sciences MAPs in theform of a short description of each MAP’s objectives. The project coordinators andpartners and the facility requirements are also listed. Table 6.8.5 lists the names of theindustrial companies participating in the MAPs.


Table 6.8.2. Future Basic-Research and MAP Experiments in the Physical Sciences

Flight/Research Facility* Flight No. of No. of Total Opportunity Year Basic MAP No. of

Expts. Expts. Expts.

Sounding Rockets Maxus-4 2001 6 - 6Maser-9 2001 1 1 2Maxus-5 2002 3 - 3Maser-10 2003 1 1 2

Shuttle-Get-Away Special PI-provided Equipment 2001 1 1 2(GAS) 2002/3 2 - 2

Spacehab, STS-107 APCF 2002 10 - 10FAST 2002 3 - 3

ISS External Platform (UF-6) ACES 2005 1 - 1

ISS US Laboratory MSL 2003 3 4 7APCF 2001 11 - 11Declic (CNES) 2005/6 1 1 2

ISS Columbus Laboratory FSL 2004/5 4 4 8EDR 2004/5 - 5 5MSL-EML 2006 3 5 8

Total 50 22 72

* Technical descriptions of the facilities can be found in Sections 5.2, 6.2, 6.3 and 6.6.

Table 6.8.5 Industrial Companies Participating in the Microgravity Application Projects (MAPs)

Belgium: Sabca

Canada: C-Core, Millennium Biologix

Denmark: Damec Research

France: Aubert & Duval, Cezus, Cime-Bocuze, Creusot Loire Industrie, Crismatec, ELF-EP, Institute Français du Petrole, Irsid, Nicox, Pechiney, Reosc, Satelec, S & CC, Schlumberger, Scometal-Creas, Sinters Robotics, Snecma, Sofradir, Three-Five Services

Germany: AEG-IM, BMW-Rolls Royce Aero Engines, Celler Pflanzen und Gewebekultur, Clondiag Chip Technologies, Cortex Biophysik, Daimer Benz Aerospace, Degussa Huels, Deutsche Affinerie, Dornier GmbH, EFU, Eisenwerk Brühl, Richard Wolf Endoscope GmbH, Escube GmbH, Esytec Energie und Systemtechnik, Federal Mogul, Helmholtz Institut für Biomedizinische Technologie, Institut für Giessereitechnik, Intospace, IP & P, La Vision GmbH, Magma, MAN-Nutzfahrzeuge, MTU, Netzsch Geraetebau, Novocontrol, Novotec Maschinen, Pari GmbH, Sacher Lasertechnik, Schunk Sintermetal Technik, Schwermetall GmbH, Siemens AG, Siemens KWU, Speed Form GmbH, TFB-Feingusswerk Bochum, Thyssen Krupp Stahl, Tital, Vacuum Schmelze, VAW Aluminium, Verein Deutscher Giessereifachleute, WAV-Giesserei, Wieland-Werke

Hungary: Duanferr Acelmuvek, Magyar Aluminium

Israel: Advanced Metal Technologies

Italy: Alenia Spazio, Bruckner Italiana, Burratto Advanced Technology Srl, Cantoni Engineering, Casti Imaging Srl, Corecom, DTM-Technologies, ENEA, ENI-Tecnologia, Ferrari SpA, Technogym Group SpA, Weidmann Plastics Technology

The Netherlands: Amersham-Pharmacia Biotech, Bioclear, Clair Techn. Monsanto, Hoogovens R & D Corp. Service BV, Organic Waste Systems BV, Shell Research and Technology Centre, Stork

Norway: Ergotest Technology, VESO Vet Research

Sweden: Aerocrine AB, Ancra ABT AB, Copytec Film Original, Erikssons Mekaniska AB,Fabri AB, HG Foton, Saab Oxelund Production Department, Sigma Design & Development, SKF Nova AB, Swedish Space Corporation, Topis AB, Westermalms Metallgjuteri AB, YoYo Technology AB

Switzerland: ABB Corporate Research, Calcom, Scanco Medical, Seyonic SA, Sulzer Medica,Swiss Metal SA

United Kingdom: Alcan, British Steel, Cyto Science, GEC Marconi IR, Gentronix Ltd., Liquids Research Ltd.,Osprey Metals, Rolls Royce Universal Technology Centre, Sandvik Steel

Many of the companies listed above are participating in two or more MAPs. 65 companies are participating in the27 life-sciences MAPs, and 87 in the 21 physical-sciences MAPs.

with funding proportional to the degree to which they are application-oriented, as forthe life sciences.

The first international AO for physical sciences, released in 2000, with a submissiondeadline of January 2001, offers scientists the use of all experimental facilities on theISS, independent of which ISS Partner is developing them or in which ISS laboratorythey will be accommodated. The international coordination of this AO is aimed atavoiding duplication of facility development, ensuring maximum utilisation of thefacilities themselves, and promoting the teaming up of researchers at internationallevel (i.e. beyond European level).

Tables 6.8.1 and 6.8.2 list the numbers of basic-research experiments and MAPsselected in the life and physical sciences, together with the required flightopportunities, facilities and desired flight periods.

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Acknowledgements

Publication of this book has only been possible because of the combined efforts of alarge number of people. I would like to express sincere thanks to everyone involved inthe writing of the contributions (see List of Contributors), the scientific and linguisticediting, and the layout and printing of the final product.

One individual, Dr. Brian Fitton, contributed to this book in a very special way. He notonly worked extremely hard on improving the language of all chapters, but alsoharmonised the various contributions in terms of content, and often improved them.I am deeply indebted to him for his efforts.

I am particularly grateful to the following ESTEC colleagues who provided constructivefeedback on the various contributions to Chapter 2: O. Minster, B. Elmann-Larsen, F. Gaubert, E. Brinkmann, D. Schmitt and P. Schiller.

I would like to gratefully acknowledge the thoughtful comments from severalcolleagues on the early versions of text on the research facilities/instruments and onthe tables that I prepared for Chapters 1, 3, 4, 5 and 6, and for the provision of someadditional figures for these chapters, in particular: W. Riesselmann, J. Ives, S. Feltham,J. Becker, G. Peters, W. Herfs, J. Vago, A. Verga, J. Castellsaguer, V. Pletser, R. Demets, H. Koenig, R. Binot, J. Schiemann, G. Reibaldi, R. Nasca, H. Mundorf and P. Manieri.

I would also like to thank those companies that have successfully derived spin-offsfrom microgravity research and instrument/facility development for providing mewith relevant illustrations and also reviewing my draft text for Chapter 3.2.

Thanks go also to H. Binnenbruck and P. Preu of DLR for reviewing my draft text on theGerman microgravity programme, and to A. Ammar-Israel of CNES for reviewing thedraft text on the French microgravity programme.

I would also like to mention the support that I received in the book’s preparation fromK. Knott, which facilitated the coordination of the efforts of the co-authors, and fromB. Battrick and his team in ESA Publications Division, responsible for the book’s finalediting and production. Last but not least, I am grateful to T. van der Putten, whocontributed significant time for secretarial work, M. Kooijmans who helped with theadministrative tasks, and P. Fornoni and T. Erickson who were helpful in providingillustrations in various electronic formats.

Günther Seibert


Prof. Dr. G.E. Morfill, Max-Planck Institut für Extraterrestrische Physik, D-85740Garching

Prof. M.V. Narici, Department of Exercise and Sport Science, Manchester MetropolitanUniversity, ST7 2HL Alsager, Cheshire, UK

Dr. P. Norsk, DAMEC Research A/S, Rigshospitalet, 7805, DK-2200 CopenhagenProf. A. Passerone, Istituto ICFAM-CNR, I-16149 GenovaProf. G. Perbal, Laboratoire CEMV, Université Paris 6, F-75252 ParisDr. M. Ries-Kautt, Laboratoire de Cristallographie et RMN Biologiques, Faculté de

Pharmacie, Université René Descartes Paris 5, F-75270 ParisDr. C. Salomon, Laboratoire Kastler Brossel de ENS, F-75231 ParisDr. G. Seibert, former Head of Microgravity and Space Station Utilisation Department,

ESA-ESTEC, NL-2200 AG NoordwijkDr. H. Sprenger, Head of Materials Science Department, Intospace, D-30159 HannoverDr. A. Tardieu, Laboratoire de Minéralogie Cristallographie, F-75252 ParisDr. P. Tesch, Huddinge Hospital, Karolinska Institutet, S-14186 StockholmDr. H.M. Thomas, Max Planck Institut für Extraterrische Physik, D-85740 GarchingProf. D.L. Weaire, Department of Physics, Trinity College of Dublin, Dublin 2


List of Contributors

Prof. Dr. K.W. Benz, Kristallographisches Institut der Albert Ludwig Universität, D-79104 Freiburg

Dr. D. Beysens, ESEME-Service des Basses Températures, Département de RechercheFondamentale sur la Matière Condensée, CEA Grenoble, F-38054 Grenoble

Dr. B. Billia, Laboratoire Matériaux et Microélectronique de Provence, Université d’Aix-Marseille III, Faculté des Sciences et Techniques de Saint-Jérome, F-13397 Marseille

Prof. R. Bouillon, Laboratory of Experimental Medicine and Endocrinology, KatholiekeUniversiteit Leuven, B-3000 Leuven

Prof. A. Brack, Centre de Biophysique Moleculaire, CNRS, F-45071 OrleansProf. R. Cancedda, Istituto Nazionale per la Ricerca sul Cancro, Centro Biotecnologie

Avanzate and Dipart. Di Biol. Oncologia e Genetica, Univ. di Genua, I-16132 GenuaDr. G. Carmeliet, Laboratory of Experimental Medicine and Endocrinology, Katholieke

Universiteit Leuven, B-3000 LeuvenDr. G. Clément, Centre de Recherche Cerveau et Cognition, CNRS/UPS, Faculté de

Médecine de Rangueil, F-31062 ToulouseProf. P.E. di Prampero, Department of Biomedical Sciences, School of Medicine,

University of Udine, I-33100 UdineProf. J. Drenth, Laboratory of Biophysical Chemistry, Rijksuniversiteit Groningen,

NL-9747 AG, GroningenProf. T. Duffar, EPM-MADYLAM, ENSHMG, F-38402 St. Martin d’HeresDr. C. Eigenbrod, Department of Combustion, Centre of Applied Space Technology and

Microgravity (ZARM), University of Bremen, D-28359 BremenProf. Dr. H.J. Fecht, Faculty of Engineering, University of Ulm, D-89081 Ulm Dr. M. Fiedele, Kristallographisches Institut der Albert Ludwig Universität, D-79104

FreiburgDr. B. Fitton, European Science Consultants, NL-2202 GM NoordwijkProf. J.M. Garcia-Ruiz, Laboratorio de Estudios Cristalográficos, IACT. CSIC – Universidadde Granada, Facultad de Ciencias, E-18002 GranadaProf. W. Grassi, Fac. di Ingegneria, Dipartimento di Energetica, Universita Degli Studi di

Pisa, I-56126 PisaDr. H.C. Gunga, Physiologisches Institut der Freien Universität Berlin, D-14195 BerlinDr. J. Hatton, INSERM U311, University of Strasbourg, F-67065 StrasbourgDr. M. Heppener, Head of ISS Utilisation and Microgravity Promotion Division, ESA-

ESTEC, NL-2200 AG NoordwijkProf. Dr. K. Kirsch, Physiologisches Institut der Freien Universität Berlin, D-14195 Berlin Prof. J. C. Legros, Microgravity Research Centre, Université Libre de Bruxelles, B-1050

BruxellesProf. D. Linnarsson, Section of Environmental Physiology, Dept. of Physiology and

Pharmacology, Karolinska Institutet, S-17177 Stockholm

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ORLD WITHOUT GRAVITY AW SP-1251 World without Gravity CONTENTS Fore word 1 CHAPTER 1. INTRODUCTION...

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